"We played the game like one more game but it is not one more game, it is a game we really need to win", said Mourinho, who said he would need to see an improvement against Young Boys in the Champions League on Tuesday if United are not to lose that game.
Meanwhile, Luke Shaw assured supporters the players are committed to helping the club recover from their poor start to the season after Mourinho accused the dressing room of lacking heart and desire after Saturday's draw.
Mourinho has often appeared downbeat throughout the campaign, as well as frustrated at a perceived lack of transfer activity, and he was unimpressed with the way his side approached the Palace game.
"There's a lethargy, in terms of the fans going into the ground, watching the game, players on the pitch".
"I think we knew the sort of the period we had all the way to Christmas, there were so many home games that three points had to be a must", United defender Smalling said.
Mourinho blames Man United's lack of heart for Palace draw
"I think Crystal Palace deserve the credit".
Manchester United's awful start to the season continued with a snooze-inducing 0-0 draw against Crystal Palace on Saturday afternoon and it is clear that new signings will be needed when the January transfer window opens. Probably the fans think José told them to start slow [in recent games] but it's the opposite.
"We have [Eric] Bailly and [Phil] Jones", Mourinho said. The team that I will play tomorrow, I want to put out a team where they can cope well with that happiness with a decisive game. "If you feel pressure, stay at home. and I don't mean stadium home, I mean home home!" I think it is only a matter of time until they go in.
But Mourinho added that it would be wholly inappropriate to suggest that his charges are not enjoying games at Old Trafford.
"It would give me a lot of satisfaction knowing that, not only are there good players here who can cause so many problems for opponents, you've even got that level of spirit and determination and guts when it comes down to it".