The Red Devils slipped further behind in the race for fourth place with a draw against the Cottagers on Sunday, and the club's record signing says the players must remain strong.
The Cottagers stunned the Red Devils as Darren Bent nodded in a 94th-minute equalizer to earn a share of the spoils, with United struggling to create clear-cut chances despite dominating possession and producing a staggering 81 crosses.
These are worrying times for United fans as the champions are nine points adrift of fourth-place Liverpool ahead of Wednesday's trip to Arsenal, but January signing Mata is confident a change in fortunes will arrive.
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"I think football is being cruel with us," the midfielder wrote on his blog. "We did everything to get the three points, but in the end this is about goals and Fulham scored in the last minute.
"It seems impossible if you look at the stats, but we couldn't win and it would have been a very important victory. But when the score is so tight you may suffer at the very end, as it happened this time.
"It was the same a week ago against Stoke City, with two players injured and one goal after a deflection. It seems that luck is not on our side, but you know that I don’t like to give excuses."
The Spaniard believes the squad needs to be more ruthless in front of goal, and believes the side's desire will eventually see it get through a turbulent phase in the club's history.
"We have to get better and improve our shooting accuracy, because we got many times to the box and could have scored more than two goals," he continued. "I'm sure we will make it. There is something we can always count on: the team's passion and sacrifice.
"We did fight until the end, and that’s what I felt on the pitch, but once again we can’t give excuses. The way to carry on is to stick together, the team and the fans, learn from mistakes and be positive, and we will show the character this team has always had."