The Atletico Madrid B captain bit the young Brazilian on the head after a clash during their Sunday match.
Vinicius Junior scored twice for Real Madrid Castilla in a reserve derby on Sunday, but his match was marred by an ugly clash with Atletico Madrid B captain Tachi.
Tachi tried to bite Vinicius Jr on the back of the head as the pair tangled off the ball, but only received a yellow card rather than a red. Vinicius Jr also received a yellow card for dissent.
This was the only blot on an otherwise excellent day for the 18-year-old, who staked his claim for a place in the Real Madrid first team by scoring both of Castilla's goals in a 2-2 draw.
After Samu Araujo had given Atletico the lead, Vinicius Jr equalised and then gave Real the lead with the goal of the game, a superb strike into the top corner of the net from outside the box. Dario Poveda salvaged a draw for Los Rojiblancos in the second half.
A performance like this must make Julen Lopetegui sit up and take notice, but the Real manager has said that Vinicius Jr will continue to play with the reserves until a first team opportunity presents itself.
The signing of Mariano from Lyon this week may push Vinicius Jr further down the pecking order in his pursuit of La Liga football.
He was on the bench for the UEFA Super Cup final against Atletico and the league opener against Getafe, but has not been in Lopetegui's matchday squad since.