After suffering defeats to Manchester City and Feyenoord, United slipped to a 3-1 setback at Watford on Sunday afternoon, but Mata has suggested that the team should focus on looking forward as they prepare for fixtures with Northampton Town in the EFL Cup and Leicester City in the Premier League.
In his blog, the 28-year-old said: "As I always say, one of the best things of football is that the game is testing you all the time.
"A win doesn't last too long, and it happens the same way with a defeat: you have the chance to make it up soon afterwards.
"Two more games this week will give us the opportunity to show on the pitch our pride and skills. There's no time for mourning. We must react."
Mata began yesterday's game on the bench after starting in United's previous four fixtures.