De Gea was left out of the squad for United's Premier League encounter with Southampton on Wednesday - with stand-in keeper Sergio Romero in outstanding form to help Mourinho's men claim a 0-0 draw.
Manchester United manager Jose Mourinho hopes Crystal Palace go "soft" on his team as he again vented his frustration with his side's schedule.
Romero's form as back-up for De Gea this season has been very impressive, giving Mourinho plenty to ponder ahead of an offseason when Real Madrid could come back in for De Gea following interest in the goalkeeper in previous transfer windows.
"[When will] David [play]?"
"David? I think the first match against (American MLS side) LA Galaxy in preseason", he said. "I think after the moment Crystal Palace beat Hull City [last Sunday] and Hull City is relegated and Swansea is safe - in that moment, our match has to be Saturday". It's a job we need to do and hopefully we can go there and do it.
The goalkeeper made several impressive stops in Wednesday night's stalemate at St Mary's, including an early penalty save from Manolo Gabbiadini, a former team-mate of the stopper's. "I don't blame myself or our decision", Mourinho said.
Icardi: "La Champions? Sì, con l'Inter. E' la squadra che amo"
Mercato Inter: a inizio giugno, la Nazionale argentina affronterà in amichevole prima il Brasile e poi il Singapore. La stagione di Mauro Icardi potrebbe essere già finita a due giornate dalla fine del campionato.
"We have the Argentina national goalkeeper and the Spanish national goalkeeper - two of the best national teams in the world". "I think for us it [the final] is the most important of the year".
"I'm really happy with both of them". They are phenomenal. And I keep saying the Portuguese kid [Pereira] is a very good goalkeeper. Southampton's wait for a home goal moved past the six-hour mark, hardly a great statistic for under-pressure manager Claude Puel.
United, who lined up with Wayne Rooney up front, went close twice in the first half, Anthony Martial dragging wide from Rooney's pass and Henrikh Mkhitaryan drawing a low save from Forster.
Having played several other fringe players against Southampton, Mourinho said the understudies had given him food for thought as he considers his team for the final.
United, criticized for playing cautiously under Mourinho, has scored just two goals in its last five games.