They recorded just five victories - the most recent being at Old Trafford in December 2013 - and lost 34 times.
United are also sweating on the fitness of Scott McTominay, Marouane Fellaini and Diogo Dalot, while Jesse Lingard remains a doubt.
Commenting on the global which are taking players away from the clubs, Mourinho said: "Some of the national teams were very professional with us and sent the players back and we could start the process early but some of them wouldn't and they kept the players. This is our ambition, as a coach and our players know this too".More news: 'He really is a liability': Tottenham fans react to Lloris red card
"Since the draw, we knew it would be a fight with Valencia for the second position and that's what we are going to try".
The 24-year-old attacker has scored 12 goals and laid on 13 assists for Atlanta United in Major League Soccer this season and has duly caught the eye of several top clubs around Europe in doing so.
However, the club's owners, the Glazer Family, appears to have finally had enough of these consistent occurrences, which is why they have asked Mourinho to keep his behaviour in check from now on, reports the Sun. "I feel that every game. Given the dynamic of the game, I didn't feel it was appropriate to bring him on". But one thing is for sure, it was a night where Manchester United found themselves on the wrong side of a gaping crater between them and Europe's elite.
"I think this season is hopefully going to be better than last season - for the team and also for myself." .