Cristiano Ronaldo ripped off his shirt and celebrated as though he had netted the winner in a World Cup final, rather than a stoppage-time clincher at Udinese that was disallowed moments later.

That was his farewell moment at Juventus, the performative Portuguese signing off with a magical thumping header that counted for nothing and a yellow card for showing the world that torso once again.

Manchester City awaited him, so it seemed, but incredibly Ronaldo is heading back to the red half of the city, back to Manchester United, providing wages and fitness prove no obstacle. Terms for the transfer have been agreed with Juve.

United have swooped for Ronaldo twice now, as an 18-year-old and at the grand age of 36. Derby day on the first weekend in November is now a red-letter day.

Ronaldo left United for Real Madrid at the end of the 2008-09 season, just weeks before Carlos Tevez swapped red for blue, pointing to a swing in the balance of power in English football.

Twelve years later and he is back in the north west, United pinching him from under the noses of City to lead their attack and the pursuit of Premier League glory.

But none of this makes sense...

Ronaldo looked a banker for a City switch before United and Jorge Mendes, the player's agent, held discussions. The Manchester Evening News reported Ronaldo's former United boss and mentor Alex Ferguson spoke to the one-time Old Trafford boy wonder, and that involvement looks to have been a moment that helped sway the now veteran striker from blue to red. Perhaps Rio Ferdinand's phone call also helped.

Pep Guardiola was expected to be cautious about the prospects of Ronaldo joining his City squad when he held a lunchtime news conference, but only out of sensible circumspection. Rather than playing a straight bat, however, he was highly pessimistic, and that was an alert that something had changed dramatically.

The BBC soon reported City had ended their interest in Ronaldo, who had instead begun talks with United, and the hints that Ole Gunnar Solskjaer dropped in United's earlier news conference grew in resonance. At shortly before 17:00 BST, confirmation arrived from United of an agreement with Juve. All this within hours of Ronaldo saying his goodbyes at Juve's training ground in the morning.

Why do United need him? They seem well stocked for strikers

Ronaldo is unmistakably in the diminishing returns stage of his career, much like Edinson Cavani whom he joins in the Old Trafford ranks. Marcus Rashford and Mason Greenwood are at the opposite end, striving to become United greats, and Anthony Martial, who should be nearing his peak years, is desperate for a run of games.

Into this battle for places walks one of the two greatest players of the past 20 years – some would say of all-time – and Solskjaer will discover his former team-mate Ronaldo still has a huge appetite for the game. His goal celebration antics at Udinese were easy to mock in light of the VAR outcome, but they showed his passion burns bright.

The data tells us Ronaldo is a fading force, but by most standards he remains a formidable footballer. He scored a decidedly healthy 36 goals for Juventus across all competitions last season, at one every 104.19 minutes. The minutes-per-goal ratio was a slight improvement on his first two campaigns with Juve, but in eight of his nine years at Real Madrid he scored at a rate better than one every 90 minutes.

He is also contributing far less in other areas of the pitch than during his prime years. Ronaldo won just six tackles last season, and only three in the league. Only five strikers with five goals or more in Serie A last season won fewer. In his 60-goal third season at Madrid, Ronaldo won 33 tackles.

Ronaldo also made 73 crosses in open play across all competitions, and 64 came in the league, the fifth-highest total of any five-goal-plus Serie A striker, but that number is far from what the former Sporting CP was producing at his career's peak. In his final season at United (2008-09) he put in 197 open-play crosses, and he topped 100 in each of his first three seasons at Madrid (2009-10 to 2011-12).

He continues to produce excellent figures, but he no longer vastly exceeds his expected goals (xG) totals and has instead almost exactly matched them in each season while at Juventus (2018-19: 28 goals from 28.3 xG; 2019-20: 37 goals from 35.84 xG; 2020-21: 36 goals from 35.34 xG).

At his best with Madrid, Ronaldo hit 55 goals in the 2012-13 season from an xG of 29.49, indicating he was far exceeding expected performance levels based on the quality of his chances.

He remains a tremendous penalty box predator and it would be surprising if he fails to hit 20 goals in the Premier League, but Ronaldo's contribution outside the 18-yard box has fallen away.

His style looked an awkward fit for City, who have sought flexibility from their front players, often favouring a 'false nine' system. Ronaldo has evolved from thrilling winger in his teens to feared targetman, and United's style is far more fitting to his game, so that aspect of the transfer makes sense.

United presumably also very much wanted him so that City couldn't have him.

What it means for United

Ronaldo gave United six years of his young career before being granted his wish to leave in June 2009, making a then world record £80million switch to Madrid.

He departed after a season where United won the Premier League and City finished 10th, with Ferguson's team also lifting the EFL Cup, reaching the FA Cup semi-finals and finishing runners-up to Barcelona in the Champions League.

Much has changed in English football, but Ronaldo is not blind to that. This represents a chance to end his career bathed in glory again in Manchester, with the Old Trafford crowd ready to worship him once more.

City won the Premier League by 12 points last season and they began this campaign as favourites to notch up another title. Signing Ronaldo would not only have hurt United deeply, but it would possibly have made this year's title race a procession.

Consider it game on now.

It was May 10, 2009, when Ronaldo last appeared in a United-City clash, scoring a deflected free-kick before being rested after 58 minutes by Ferguson as the Red Devils scored a 2-0 Old Trafford victory.

Ronaldo left the field in frustration, wanting to play for longer, but days earlier he had been the prime architect of the famous 3-1 win at Arsenal in the Champions League semi-finals, and Ferguson wanted to save his star asset for the tests ahead, particularly the European final against Guardiola's Barcelona.

Now the long-retired Ferguson's influence tells once more. He persuaded Ronaldo to take his United career into extra time during his first stint at the club, and now the man Jose Mourinho describes as Solskjaer's 'big boss' has struck again.

Messi v Ronaldo: The reunion's off!

The great rivalry between the standout players of their generation looked set to be rekindled in the Champions League group stage, with Ronaldo's City taking on Messi's PSG. Scrub that now though. Any such clash will have to wait for the knock-out rounds, with United having Villarreal, Atalanta and Young Boys to negotiate in their pool.

This announcement tells us United are craving Champions League success again. They have won the competition three times, while Ronaldo has done so on five occasions, once with United and four times at Madrid. In three years at Juventus, he could not drag the Old Lady of Italian football to European glory, however, a disappointment given that had been ostensibly why he was signed.

United's owners, the Glazer family, will expect the investment in Ronaldo to pay off handsomely, given his commercial appeal and United's global reach. And the  Glazers even stand to earn a little rare kudos from supporters who are bound to get misty-eyed at this deal.

Signing a five-time Ballon d'Or winner will be interpreted as taking a short-cut to glory. It is a gamble too though.

Two Scudetti in three years at Juventus was one fewer than Ronaldo may have expected to take away from Turin, given Juventus were on a seven-in-a-row streak when he joined, and the coach who delivered the second of those titles, Maurizio Sarri, recently spoke of the challenges involved in accounting for the Portuguese's imposing presence.

Sarri told Sportitalia in July: "The management of Ronaldo is not easy, he is a multinational that has personal interests to match those of the team. It is certainly a difficult situation to manage."

But Sarri ventured that there were "many positive aspects because at the end of the year Ronaldo brings important results".

The ego has landed, back in Manchester, back in red. It's one-nil to Solskjaer and his big boss in the season's first battle of Manchester, and the rest of the campaign should be a thrill ride.