...so Louis van Gaal really needs to get his thinking cap on. Does he abandon his favourite formation to make room for Adnan Januzaj? It's also big for Arsenal's Germans and Big Sam.
After the departures of Diego Costa, Filipe Luis and Thibaut Courtois to Chelsea, plenty are saying Atletico Madrid won't retain their title. Tim Stannard thinks otherwise...
A reminder of Chelsea's past managerial history, if you will. In the time between Jose Mourinho leaving the club and returning last summer, only one manager actually managed at Stamford Bridge for an entire season. That was Carlo Ancelotti, sacked after finishing second in the Premier League and exiting the Champions League at the quarter-final stage to a Manchester United side that were defeated in the final by Barcelona.
This season, Mourinho's Chelsea are third favourites in the Premier League with six games remaining, and on Wednesday night lost the first leg of their Champions League quarter-final in the Parc de Princes. It's not a drastically different record to Ancelotti's, I'm sure you can agree.
Mourinho has never before failed to get beyond this stage of the competition, and a 2-1 away defeat would not have been a catastrophe. In ten of the 18 occasions a side has lost the first leg 2-1 away in the Champions League era, that deficit has been overturned at home, and Mourinho would have remained confident of ensuring progression. Javier Pastore's last-gasp goal changes the mood entirely.
Chelsea have now won just one of their last seven away games in all competitions, and that was a two-mile saunter down the road to Craven Cottage to play a doomed Fulham side. This was another defeat and performance that felt distinctly un-Mourinholike, with the goals conceded not through the brilliance of the opposition but due to defensive lapses. At this stage of the season, these aren't slip-ups that Mourinho usually allows his side to commit, but amongst all the mind games and shifting of blame away from his players, the cracks are truly beginning to appear.
This defeat will be particularly frustrating for Mourinho because Chelsea had been able to recover from initial adversity. After 15 minutes, the Portuguese would have been a worried man, John Terry's weak header presenting the ball to an emphatically grateful Ezequiel Lavezzi, whilst Ramires had continued a worrying trend of indiscipline with a crude challenge on the same player, earning him the booking that will cause the Brazilian to miss the second leg. Without the cup-tied Nemanja Matic, it looks a monstrous task.
And then PSG stopped playing, suddenly losing their forward momentum and verve, instead preferring to operate a safety-first mindset that revealed their satisfaction in taking a 1-0 scoreline to Stamford Bridge next Tuesday.
There is evidently nothing intrinsically wrong with such a defensive approach against a side set up for the counter attack such as Chelsea, and with Eden Hazard, Oscar and Willian all capable of attacking at speed Laurent Blanc evidently felt that the 'closed shop' strategy would be successful - this was quite obviously a pre-planned tactic.
Unfortunately, the prosperity of such a tactic relies entirely on both caution when in possession and patience in defence, neither of which PSG demonstrated. Inattentiveness led directly to Chelsea's equaliser, Marco Verratti losing the ball in midfield before Thiago Silva compounded the error by diving in at the feet of Oscar. The Brazilian made the most of the contact but it was a stonewall penalty, converted with typical ease by the ever-impressive Hazard.
But, just as at Selhurst Park on Saturday (and at the Britannia Stadium and Villa Park in recent times), Chelsea shot themselves in the foot. David Luiz fulfilled his reputation as the ultimate curate's egg footballer with a rash and unnecessary foul on Blaise Matuidi and, when the cross was delivered from Lavezzi, Luiz could only help it into his own net. In stoppage-time came the ultimate frustration, Pastore allowed to dance free from three players on the right-hand side of the penalty area. Misery compounded.
When asked after the match who was at fault for the defeat, Mourinho was in a defensive mood: "Don't ask me to tell you that. I can't do that with you. I have to do it inside, not outside." On the defending for his side's goals, the Portuguese was more honest. "You say sloppy," he said. "I say ridiculous."
"A little horse that next season can race," was Mourinho's assessment of Chelsea in February. On current evidence, that horse is rather limping towards the end of the season. Surely the jockey must take some of the blame?
Daniel Storey - Follow him on Twitter.