The forward has not played for Real since suffering a thigh muscle injury during a 1-0 win at Celta Vigo last month. He also missed Brazil's 2026 World Cup qualifiers against Bolivia and Peru.
"Vinicius trained with the team yesterday, he's in good shape," Ancelotti told reporters ahead of Sunday's game at the Metropolitano Stadium.
"He trained very well today and he'll be in the squad. We'll decide tomorrow on what role he is capable of playing."
Defender Dani Carvajal (31) would not be available for selection, Ancelotti added.
On Sunday, Real face an Atletico side that lost 3-0 to Valencia in their last league clash, but Ancelotti said the defeat will not have any bearing on the match.
"The derby is a great opportunity. They are always special games," he said.
"It's the two big teams in the capital, there is so much quality on show. They are always very intense games, great to watch. I don't think the fact they lost to Valencia will have an influence on the game."