By Graham Ruthven (@grahamruthven)

The Champions League is back, and now it’s time for the real stuff. 32 has been reduced to 16, with Europe’s biggest and best targeting continental glory at the San Siro in May. This is when the good stuff starts.

Barcelona, Bayern Munich and Real Madrid appear to be frontrunners to lift the famous trophy in Milan, but there are a number of other contenders in the competition. Here are five questions ahead of the round of 16.

Can Chelsea salvage their season in the Champions League?

This season was written off at Stamford Bridge long ago. When Chelsea fans recall their fondest memories of the past decade or so, the 2015/16 season will be forgotten as quickly as possible. But the Champions League offers the Blues the opportunity at redemption.

Of course, Guus Hiddink picks up where Jose Mourinho left off on the continent - with the Special One no longer special enough to keep his job on the King’s Road. Chelsea suffered defeat to PSG at this stage of the competition last year, facing the French champions for the third successive year. Will it be a case of better the devil you know?

To what extent do Real Madrid’s hopes rely on the fitness of Gareth Bale?

Nobody at the Santiago Bernabeu will admit it, but focus has turned to the Champions League at Real Madrid. The Spanish Liga title race is far from settled, but there is an unspoken acceptance that the championship will once again be Barcelona’s come May. And so Europe is where their season will be defined.

Real Madrid feels like a club in something of a transition at present, though. Cristiano Ronaldo is still the star of the show, but his importance to Los Blancos is waning somewhat, with Gareth Bale instead starting to have more of an influence on Zinedine Zidane’s side. The Welshman’s fitness has been an issue this season though - Real Madrid’s Champions League hopes might depend on whether he can avoid injury.

Is there any team that can stop Barcelona?

No team has successfully defended their European Cup title since AC Milan in 1990. But Barcelona look ready to test that particular record, with Luis Enrique’s side arguably even better now than they were when they beat Juventus in Berlin last year. So can anyone really stop them?

Real Madrid have certainly failed in that respect domestically, and so most have anointed Bayern Munich as Europe’s only potential Barca beaters. Pep Guardiola’s knowledge of his former side could stand the Bavarians in good stead, but nonetheless, Barcelona are playing at a level like no other right now. At this standard, the Champions League might already be something of a foregone conclusion. 

Would Pep Guardiola’s Bayern Munich reign be a failure without Champions League success?

Things have grown slightly tetchy in Germany since Guardiola confirmed his impending exit from Bayern Munich at the end of the season - when he will take over at Manchester City. The German press have been very critical of the Spaniard, with his legacy in Bavaria already under scrutiny before he has even completed it.

Guardiola took over at Bayern Munich on the back of a treble-winning season under Jupp Heynckes, with some claiming that he has in fact taken the club backwards in three years. The only thing that might stave off such conclusions is glory in this season’s Champions League. Guardiola’s reputation might rely on whether his team not only makes it to, but wins, in Milan in May.

Can Manchester City finally make the breakthrough into the elite?

Ever since Manchester City won the Premier League title for the first time, nearly four years ago, the next step for English soccer’s most ambitious club has been clear. With the financial might of Abu Dhabi behind them City have their sights set on the very top of the European game. 

But for the money that has been spent over the years, the Citizens have never made it past the Champions League’s last 16 stage in four attempts, finding it rather difficult to break into the sport’s elite. Can they finally push past that threshold? Manuel Pellegrini doesn’t have long left in the dugout, but he could still leave a lasting impression.