Injury-hit United face Celta Vigo in the semi-final of the competition, knowing that a triumph over two legs will see them through to the Stockholm final where they have the chance of securing a Champions League spot.
The Palace game comes three days before the Europa League final, and Mourinho would have no qualms in allowing Nicky Butt's team to take to the field at Old Trafford on the final day of the league season.
He told reporters: "If we beat Celta, we have the final and, in this moment, it is obviously hypothetical.
"The Europa League final is on the Wednesday and we play against Crystal Palace on the Sunday. Before that, we play Southampton away a few days before, so we would be playing the final with disastrous consequences.
"So, again, maybe this result is also a blessing because maybe I can bring Nicky Butt and his team to play against Crystal Palace and hopefully they [Palace] don’t need the game to stay in the division because it would be very, very bad if they needed the points and we played with the Under-23s."
United are currently on an 11-game unbeaten run but find themselves a point behind Manchester City in the race to finish in the top four.