Vinicius was bitten by Tachi during Castilla's draw with Atletico.
"It's a reaction that came under the high pressure of the match," Tachi began to the club's official website.
"I'm not proud of what happened and it does not reflect anything about me as a player.
"This action is not representative of anything instilled in us by the academy and I know it is not an example for people watching at home to follow. It does not represent the way I play and it is a pity that this action has taken prominence and eclipsed a good game from us against Castilla."
Oddly, the incident happened right under the nose of the referee, who saw it fit to book both players.
"At the end of the game I spoke to Vinicius," Tachi continued. "We gave each other a hug and everything was left there.
"Now I have to learn from this and move on."