Claudio Ranieri's side are rock bottom of the Premier League table despite picking up a point against Leicester on Wednesday but the Portuguese full-back has already learned there are no easy games for United, who have not won any of their last four league matches.
"When the team is defensively stronger and doesn't need people in midfield to give balance to the team, rather than being involved in creation and attacking dynamically, I think the horizons for Fred change completely", Mourinho said.
"Fulham is a big game now".
The Red Devils have only collected 23 points in their opening 15 games in the Premier League to highlight their inconsistent form in Jose Mourinho's third season in charge.
Heather Nauert 'to replace Nikki Haley as USA envoy to UN'
Haley unexpectedly announced her resignation in October and promised to serve in her role through the end of 2018. All the while, she stayed in the good graces of the White House, even as Tillerson was increasingly on the outs.
Manchester City vied with United for Fred's signature but, like January acquisition Alexis Sanchez, Pep Guardiola's men may well be thinking they have had a lucky escape. The 47-year-old said, "Not frustrated, for example, he (Kolasinac) was coming at the end of the match with his head looking down".
"Especially this month there's a lot of games, so we need everyone in the squad to be fully fit".
The Gunners looked as potent as ever when they went forward against Manchester United, but were shaky at the back and seemed to switch off at crucial times.
After the game, while speaking to reporters, Arsenal boss Unai Emery was asked whether he felt "frustrated" at the result and the manner of the draw but the Spaniard responded brilliantly.
"Everyone at the club will now be working as hard as we can to ensure Rob is back on the pitch as soon as possible".