After days of speculation that the Portuguese superstar would return to the Premier League with United's bitter rival Manchester City, Ronaldo stunned everyone with the news his former club will actually be his next next destination.

"Manchester United is delighted to confirm that the club has reached agreement with Juventus for the transfer of Cristiano Ronaldo, subject to agreement of personal terms, visa and medical," a statement from the club read on Saturday (AEST).

The deal is reportedly worth £12.8 million ($24.2 million) plus £6.9 million ($13.1 million) in add-ons.

Ronaldo was pictured leaving Juventus training late on Friday, having reportedly said his goodbyes to team-mates, as most thought the 36-year-old was headed to City.

Massimiliano Allegri later confirmed he would not be selected for the home Serie A fixture against Empoli on Sunday (AEST) after having told the Juve boss he wanted out.

"Yesterday, Cristiano told me that he no longer has any intention to play for Juventus. For this reason he will not be called up for tomorrow's game," Allegri said.

"Things change, it's a law of life. Juventus remains, which is the most important thing. Cristiano gave his contribution, he made himself available, now he leaves and life goes on.

"Cristiano is to be thanked for what he has done, also as an example to the youngsters. But as I said, we must go on."

Ronaldo spent six years at United previously from 2003 to 2009, scoring 118 goals in 292 games for the club and winning his first Premier League title in 2006-2007. He left for Real Madrid in what was a world record transfer for £80 million. He played 438 matches for Los Blancos, scoring 450 goals, before he moved to Juventus in Serie A, where he has made 134 appearances for the Old Lady for a return of 101 goals. 

The five-time Ballon d’Or winner has so far won more than 30 major trophies, including five UEFA Champions League titles, four FIFA Club World Cups, seven league titles in England, Spain and Italy, and the European championship for Portugal.