The Spanish goalkeeper missed United’s 3-0 win over Sunderland through injury and was replaced by Sergio Romero, who is expected to remain in place for Thursday’s Europa League quarter-final first leg away to Anderlecht.
“He has a problem with his hip," Mourinho said of De Gea. “When he dives, he feels it a little bit. It's good for him to have a rest.”
“It's good for Sergio Romero to play before Brussels. De Gea will probably be fit for Chelsea. Yes, if he's in good condition.”
United did not miss their No.1 in a convincing win over relegation-threatened Sunderland, Zlatan Ibrahimovic striking home in the first half before Henrikh Mkhitaryan and Marcus Rashford secured the three points.
Victory took Mourinho’s side above Arsenal and into fifth, though they will be back in sixth should Arsene Wenger’s side win at Crystal Palace on Monday.