Chelsea, suffering a mid-season slump that has seen them win just one game out of the last six in the Barclays Premier League, have been ordered to return to the free-flowing football that excited everyone when the new campaign began.
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Ancelotti was clearly angered and upset by Chelsea's 1-1 draw against Everton last Saturday and told his players so in a team meeting.
With Chelsea have already finished top of the pool, and Marseille through in second, there is little but pride riding on tomorrow's game, but the Italian coach made it clear he wants his side to go back to the style of football which brought them a flood of goals and five straight wins at the start of the Barclays Premier campaign.
"We are trying to search the right way to move on quickly from this moment and we have a possibility to do this tomorrow," said Ancelotti.
"The result of the game is not important but the performance is very important. We want to put out the best line-up possible because we consider the game important for our confidence and to come back and play our football.
"We have to come back quickly to play our football. I spoke with my players. It is not the right place to explain what I said to them. it was private and confidential. The reaction has to be good tomorrow.
"When I say strong team, it doesn't mean there are no young players in the team. Maybe some of them will be involved. We give a lot of importance to this game for the reason that we need to come back to play our football."
Meanwhile, Didier Drogba will make an emotional return to the Stade Velodrome and admits finishing his career at the club remains a very tempting prospect.
Drogba, now 32, spent just a year at Marseille, scoring 18 Ligue One goals, plus another 11 in Europe in 2003/04 after arriving from Guingamp.
His goal record made him a cult hero among the Marseille fans and the Chelsea ace has often spoken of finishing his career back at Stade Velodrome.
"I am glad to be here and see some familiar faces," said Drogba.
"I know that everything will be good tomorrow. All I can say is that I have been at Chelsea for six years now and I am happy there.
"My family is also happy there. Of course Marseille is tempting. But there are so many parameters that come into play. I can see myself ending my career at Chelsea."
OM coach Didier Deschamps is hoping Drogba's love for the south-coast club will inspire him to play for them once more before he retires.
"Every coach appreciates Drogba," said Deschamps.
"If you know a coach who doesn't rate him, maybe you can introduce them to me. He's someone everyone would want to have in their team. He's a player of a very high calibre who had one great season at Marseille and the supporters took him to their hearts, which isn't easy.
"But tomorrow he's an opponent who, as he's said before, is very attached to Marseille and maybe one day will wear the shirt again. I don't know if that's feasible or not, who knows."
Meanwhile, Marseille goalkeeper and captain Steve Mandanda is relishing the match.
"It's my first Champions League game without pressure, we've prepared well and it'll be a decent game," said Mandanda.
"We know we're going to play a big team tomorrow. Maybe for the fans it's like an exhibition match but for the players it's still an important game. There's not too much pressure but it matters to us.
"Whether it's Drogba in front of me or whoever it is, my aim will be the same, to keep a clean sheet. I'm not focusing on Drogba especially."