The top-of-the-table Blues host domestic title rivals United next weekend in a match which could eventually prove crucial in the race for league silverware.
But before that Ancelotti's side travel to Spain to take on Atletico when a win would guarantee a place in the knockout stages of the UEFA Champions League.
The Chelsea boss therefore wants his players to remain focused on their European commitments before turning their attention to United.
"Usually all the people think about the game against Manchester United but we have another important game during the week and we want to prepare well," said Ancelotti.
"It is very easy to prepare for Manchester United because it is a very important match, but we need to maintain concentration in the Champions League at this moment."
Meanwhile, Ancelotti insists Didier Drogba is 'ready to work for the team' as the Ivory Coast international prepares to make his European comeback against Atletico following his suspension.
Drogba was forced to serve a three-match ban following his foul-mouthed confrontation with Norwegian referee Tom Henning Ovrebo at the end of Chelsea's Champions League semi-final defeat by Barcelona in May.
"I didn't know what happened (last season). I saw what happened. I didn't speak with him about this, I'd rather speak about the results of the last three games," said Ancelotti, whose side have recorded wins of 5-0, 4-0 and 4-0 since defeating Atletico 4-0 at Stamford Bridge a fortnight ago.
"I told him to prepare for his return tomorrow. Tomorrow he will return to work for the team - and he is ready to work."