The Brazilian winger, key for Madrid this season, has been shut down by Barca defender Araujo in recent clashes with the Catalans, with coach Xavi Hernandez deploying the centre-back on the right to directly confront him.
Vinicius has scored twice in 12 games against Barcelona, both times before Araujo started at right-back.
No player has scored from open play against leaders Barca at Camp Nou in La Liga this season, giving champions Madrid a formidable task as they try to eat into their nine-point deficit.
"He's had more difficulties than in other games, but Vini is always Vini, his mobility can help him get the best (from himself) in tomorrow's game," Ancelotti told a news conference Saturday.
"I'm thinking of putting him on the right, let's see. He can play on the right, Vinicius."
Ancelotti later said he was joking about using Vinicius on the right flank, but reiterated that the forward could be given more liberty to drift from the left.
"Obviously that wasn't serious, but mobility could be important, not having a fixed reference point. Speaking generally, against a forward that's another problem for a defence.
"Vini will play on the left, with more mobility."
Xavi also looked forward to the battle between Araujo and Vinicius.
"Araujo is very physically strong, he's quick, fast, and understands the movements of his opponents," Xavi told reporters Saturday.
"He's responsible, and a leader. He's a world class defender, one of the best in the world. Having Ronald in the team, is a guarantee, an advantage.
"Usually when he takes on Vinicius, he comes out as the winner of the battle, but Vinicius can make a big difference.
"It's not just Ronald, it's (everyone) looking out, and collectively, we've been very good against Madrid."
Xavi said he was looking forward to coaching in the Clasico at Camp Nou for the first time, with his prior clashes with Madrid all taking place away from home.
"I am very motivated, you know I'm a big Barca fan, these games get me going," added Xavi. "It's my first Clasico at Camp Nou (as coach), I'm excited, I'm motivated."
Barcelona beat Real Madrid 1-0 earlier in March in the Copa del Rey semi-final first leg at the Santiago Bernabeu.
The visitors put on a defensive masterclass while Madrid had more of the ball, earning Xavi some criticism for betraying the club's preferred style of possession football.
Barcelona were without several key players for that game, including Robert Lewandowski, Pedri and Ousmane Dembele -- the latter two of whom are still out for Sunday's derby.
The league leaders have also won 1-0 in the top flight nine times this season, keeping 19 clean sheets in 25 games.
Atletico Madrid coach Diego Simeone even had a dig at Xavi, noting how some "lovers of the beautiful game" can now be heard saying 1-0 is an attractive scoreline.
The Barcelona coach responded saying that while he respected his Atletico counter-part, winning by a goal in the Clasico would be a "marvellous" result.
"What problem is there with 1-0? Barcelona won their first European Cup (in 1992) with (Ronald) Koeman's goal, 1-0, and nobody said anything," added Xavi.
"I'd prefer a 4-0, a 5-4, but it's hard to score goals, people defend well, people who haven't played the game can't understand it. Winning 1-0 is a marvellous result."
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