Chelsea have announced that Alex will delay surgery on his knee to feature against Birmingham on Saturday, while John Terry could be available for Tuesday's Champions League game against MSK Zilina.
Chelsea lose injured John Terry for a month
The Blues were facing a crisis in central defence after the announcement that Alex faced two months out after knee surgery and Terry could be sidelined for months with a nerve problem.
Branislav Ivanovic and Paulo Ferreira played at centre back in the Blues' shock 3-0 defeat at home to Sunderland last weekend, and youngster Jeffrey Bruma was expected to come in to face Birmingham.
However, Chelsea have now announced Alex - an unused substitute for Brazil in their midweek friendly defeat to Argentina - will play at the weekend before undergoing surgery.
"Alex will be available to play. This is good news. He trained with the Brazilian team," Ancelotti said. "We know that he needs to have the surgery.
"We are in a position that we can procrastinate [over] this but we know that he needs to have the surgery. He trained after the meeting with the Brazilian doctor and was on the bench, so it's not a risk. It's not a risk but his knee needs to be cleaned."
Alex added: "I need surgery, and maybe after the game I will go to Brazil and do the operation on Thursday. Arthroscopic surgery is easy to do, and I can play on Saturday to help the team. We have too many players injured, so I said to the coach I can play. I am not 100% fit but I can play."
Ancelotti also revealed at his press conference that John Terry's problem has been identified and the captain could make his return to action on Tuesday.
"There's a muscle on John's leg, the piriformis muscle, and the nerve moves, so he feels pain," he said. "He will not be involved in the game tomorrow but maybe it can happen that in the next game he will be able to play.
"Because he has pain he is not able to play and for us he is a very important player but I think we can move on this problem quickly - we have to move on this problem quickly and put John in the condition to play.
"If he is not 100%, he has experience, he has ability to play fantastic football, to give fantastic support to the team. He did last year because also last year he had some problems but everything was under control.
"It's difficult to have a player 100% fit. I played for 20 years - I don't remember how many times I was 100% when I played. Sometimes - always - you have some problem."
Asked if Chelsea would look to bring in defensive cover during the transfer window, Ancelotti said: "It depends what happens with Alex and in the next few days with John Terry. Obviously, if both players are not able to play for a long time, I think we have to think about this, but just in that case."
Chelsea will be without Yuri Zhirkov against Birmingham, but Florent Malouda is set to start.