Fulham were held to a 1-1 draw with Leicester City at Craven Cottage in mid-week, after Claudio Ranieri won his first game in charge of the Cottagers following a 3-2 win against Southampton at the end of November.
"There have been more rumours of Jose Mourinho leaving Manchester United", read the statement.
A point against Arsenal left United without a win in four Premier League games ahead of Fulham's visit to Old Trafford on Saturday.
The manager then elected to use Herrera and Nemanja Matic in front of a five-man defence against Arsenal, with Pogba and Fellaini relegated to the bench.
Mourinho said Fred was adapting "step by step" to life in the Premier League and added: "You have other players in other clubs that needed time (to adjust) and you have some of them that play even less than Fred is playing".More news: Philadelphia 76ers guard Markelle Fultz diagnosed with nerve condition in his shoulder
"When the team is defensively stronger I think the horizons for Fred change completely".
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.
Asked about Fred's adaptation, Mourinho said: "You know, step by step".
"But I prefer to say the team as a team had that mentality and we have to try to transport to this game (against Fulham)".
"I want to be positive and think we are going to win but if we don't, then we must give credit to the people that deserve credit", Mourinho said.
Arsenal are a good side, but they're due a downturn in results, this sort of thing won't happen all season.