The 34-year-old appeared to trip the Spaniard before shoving him in the back in the 86th minute during the FA Cup clash at Old Trafford.
The FA will analyse footage of the incident before making the decision, but the Blues interim manager Rafael Benitez refused to comment on the incident.
"I haven't seen the replay - you can see the replay," Benitez told Sky Sports News. "You have an advantage and can do it now.
"I don't talk about things that happen on the pitch."
The winner of the quarter-final replay will meet Manchester City at Wembley in the last four of the competition.