A bridge too too far for Liverpool or will Chelsea suffer the crushing blow of another semi-final disaster within touching distance of their European dream?

No one can answer that with any certainty, but what I do know is that one player who will step out onto the Stamford Bridge pitch tonight owes the Chelsea fans a big performance.

At his best, Didier Drogba is one of the world's most formidable strikers. But, like many of his ilk, he comes complete with a massive ego and unfortunately we have seen more of that this season than his outrageous talent.

There is an old saying in football that if you are going to be high maintenance then you had better be good, and in the last couple of games Drogba has been as poor as I can remember him. Away at Liverpool last week and at Stamford Bridge against Manchester United on Saturday, his contribution was minimal.

That farcical episode when he stood there arguing with Ballack over the free-kick against United was a joke. His ego was out of control and it was beyond belief when his tantrum continued on the touchline with Steve Clarke and other players. Perhaps, on reflection he thinks he behaved stupidly, or maybe he still thinks he did nothing wrong and was right to throw his rattle out of the pram.

Tonight he has to step up to the plate and put in his best performance of the season. I know he hasn't played a lot of games for Chelsea this year and that can't have helped and he was obviously hit hard by the departure of Mourinho but when a professional footballer gets paid around £100,000 a week, you work for the club - not an individual manager.

Everyone thinks he will be out the door in the summer, but in the meantime he would do himself a power of good to get his act together tonight and show he is a class performer and not a clown.

On the opposite side of the coin, Michael Ballack looks to have found his form and self-belief at the right time for Chelsea. It's not been easy for him. He struggled to come to terms with Premier League football and suffered a bad injury. But he stuck in there, ignored all the speculation about his future and has emerged as one of Chelsea's most important, if not the most important player for this game. We are now seeing a fit and confident Ballack and he could be hugely influential, particularly if Frank Lampard is missing. If Lampard does play, then Chelsea will have two forward-thinking players in midfield who can score while Liverpool will play with two central midfielders but only one going forward, so that could be the difference. Liverpool's poor record at Stamford Bridge won't matter. Benitez knows that his team have to score, but I still don't see him picking anything but a cautious side to start with.

When they played Chelsea in the League at Stamford Bridge earlier this season, Liverpool had Peter Crouch up front with Steven Gerrard just off him. They had twice as many shots as Chelsea then while staying tight at the back, and I think Benitez will remember that. He will know that with Torres instead of Crouch he has a player better equipped to take the chances. Torres didn't get going in the first leg at Anfield, but his movement, his ability, his strength and his finishing makes him the man Chelsea have to keep quiet if they are to get into the final.

It's almost impossible to divide these two teams, but it's in midfield where the battle could be won where I would expect to see Javier Mascherano, Xabi Alonso and Gerrard up against Claude Makelele, Ballack and possibly Lampard.

Gerrard is hugely important to Liverpool and, tonight, I think he will be asked to play just off Torres which should allow him a little bit more space to influence the game.

Chelsea will not come out of the traps at 100 miles an hour like they did against Manchester United on Saturday. They have a 1-1 in the bank and a 0-0 draw would do them nicely, so they will be looking to take minimal risk. But my hunch is that Liverpool will score, and the game will end 1-1 and go to penalties.

If that happens it's going to be the team that handles the pressure best, and we all know Ballack will be the first name on the Chelsea list of penalty-takers.

Andy Gray co-commentates on Chelsea vs Liverpool, available on Sky Sports2, Sky Sports HD2 and via Sky Broadband. Goal updates via 24-7 mobile.