The Brazilian has been out since suffering a hamstring injury against Celta Vigo on August 25th but has recovered quicker than expected.
Vinicius, 23, may start on the bench in the Madrid derby at the Metropolitano where league leaders Real Madrid are looking to maintain their 100 per cent start to the season.
"Vinicius trained yesterday with the team, he's in good condition, the injury is forgotten, he trained today very well - he will be in the squad," said Ancelotti.
"Later, we'll decide what role he has in the game tomorrow."
The Italian coach did insist the club would take no risks with Vinicius.
"He trained yesterday because the risk was zero, he trained today because the risk was zero," said Ancelotti.
"If tomorrow there is one per cent risk, we won't play him.
"The important thing is that Vinicius has recovered, he's lacking a bit of match fitness but that's normal, they are things we'll evaluate tomorrow."
Last season a group of Atletico fans caused outrage with racist chants outside their stadium aimed at Vinicius before the derby clash in La Liga.
In January, Atletico supporters hung an effigy of the forward near Real Madrid's training ground, with four fans later fined and banned from games.
"I think that something has changed after last year ... there's a more calm, respectful atmosphere, and I think tomorrow will be the same," continued Ancelotti.
Ancelotti confirmed midfielder Jude Bellingham was fit for the game after a brief illness troubled him in the week, but Dani Carvajal was still out with a leg problem.
Atletico, seventh, have struggled at the start of the season and were beaten 3-0 last week by Valencia in what their coach Diego Simeone described as the "weakest" performance of his reign.
"Derbies are great opportunities," added Ancelotti.
"They are special occasions. These are two teams from the capital, two teams with great quality, the game will be very high intensity."
Atletico coach Diego Simeone believes his team can compete with their city rivals, despite the two sides' differences.
"Madrid and Barcelona can always afford to have great players, but we've always been able to compete with them," said Simeone.
"So we have to concentrate on ourselves and continue to compete with them as we have done for the last 11 years."
Atletico have various injury problems, including Thomas Lemar who will be out for months after rupturing his Achilles tendon last weekend.
"As (Pep) Guardiola (the Manchester City manager) said, there are a lot of matches, a lot of travelling, three international breaks before December... but we have to adapt as best we can to this situation," added Simeone.
