Vinicius has missed his side's last three matches with a muscular problem, and he will also sit out Saturday's league game with Girona, but the Brazil international is back in first-team training much sooner than expected.
Ancelotti said on Friday that, barring any unforeseen setbacks, Vinicius will be available for the Champions League game against Atalanta, which is a must-win fixture for the European champions.
Real Madrid are only just clinging onto a playoff spot in the Champions League table, with a disappointing campaign to date seeing them pick up just six points from their five matches to sit down in 24th.
Ancelotti also revealed that David Alaba is on course to make his return from a serious knee injury in January.
Ancelotti confirms Vinicius boost ahead of Atalanta game
"It's great news. We're encouraged to see how well Vini Jr. has recovered from his injury. He won't be available tomorrow but he should be ready for our next Champions League game," said the head coach.
"We're delighted to have Alaba back in training too. He needs all of December to ensure he's fit and ready to play again in January. He'll keep working individually and we'll bring him back into the group gradually. His comeback is set for next year."
Dani Carvajal and Eder Militao are out for the season with serious knee injuries of their own, but Eduardo Camavinga is also closing in on a return, with the 22-year-old, who has been out with an ankle problem, likely to be back before the winter break.
Real Madrid will enter Saturday's clash with Girona off the back of a 2-1 defeat at Athletic Bilbao, with the result leaving them second in the La Liga table, four points behind leaders Barcelona with a game in hand.
Ancelotti only "mildly concerned" with Real Madrid's poor form
Real Madrid have lost four of their last seven games in all competitions, but Ancelotti said that he is only "mildly concerned" with his side's struggles of late.
"We're still in the fight in every competition. We have to keep that optimism you need, considering the problems we have and those we've encountered so far. We're optimistic because we've got a brave, top quality squad. We haven't shown our best form so far but we're convinced we'll get there sooner or later. I would say I'm just mildly concerned," he added.
"Tomorrow's game will be another difficult one. Girona are doing a good job, they're having to contend with the Champions League this year too, but they always compete well. We have to treat it as a chance to get back to winning ways, and remain in the mix for La Liga.
"I have to accept it (criticism) because the team is not at its best. As always in football, the responsibility for that falls to the coach, so he's the one who faces the greatest criticism. That said, I think you're being a bit too harsh. Perhaps that means you're fed up of me.
"I'm not tired of this job, despite the criticism, I'm still delighted to show up here every day. It's to be expected, I understand it. Just like stress, sometimes criticism helps fuel the fire and pushes you to do a better job."
Real Madrid have only won three times on their travels in all competitions this season, suffering defeats in their last two, and they will be visiting a Girona side that are unbeaten in their last four La Liga matches.
Written by
Matt Law