There had been some concern over Bellingham's involvement when he was forced to leave training early on Friday due to a stomach problem.
However, the England international, who has scored six times for Los Blancos this season, trained normally on Saturday and will be available for the La Liga game with Diego Simeone's side.
Vinicius will also be in the squad, with Ancelotti revealing that the Brazil international «has 100% recovered» from the hamstring issue that has kept him out since the end of August.
«He will be in the squad for tomorrow's game,» the Real Madrid boss told reporters during his pre-match press conference when asked about the forward.
«There is zero risk. He trained yesterday because there was zero risk. He trained today because there is zero risk. If we think there is one percent risk tomorrow, he won't play.
»What's important is that Vinícius has recovered. I've told him that he's missing some conditioning after a month out, but we'll evaluate it tomorrow."
Meanwhile, when asked about Bellingham, Ancelotti denied that there was ever a real risk of the summer arrival being unavailable for selection against Atletico.
«No, it's just a story, he didn't feel good on Thursday but he has trained normally today and he'll be good to play,» he added.
Dani Carvajal will definitely be absent on Sunday alongside Thibaut Courtois and Eder Militao, while Arda Guler is not expected to be involved despite returning to training following knee surgery.
Ancelotti was also asked about his midfield options for Sunday, with Luka Modric and Toni Kroos widely expected
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