Veteran goalkeeper Edwin van der Sar has issued a warning to Manchester United's title rivals.
Back-to-back Premier League defeats for United have given Liverpool and Chelsea renewed hope they can catch the defending champions.
Liverpool are now just a point behind United with eight games left, and although the league leaders have a game in hand, the Reds could regain top spot on Saturday with United not playing Aston Villa till Sunday.
That seemed unthinkable a few weeks ago with United charging seven points clear as Van der Sar set a new record for the number of minutes without conceding a league goal.
But the 38-year-old Dutchman believes the successive setbacks against Liverpool and Fulham make Sunday's visit of Villa a must-win game.
"The Villa fixture is a massive game for us," he told the Manchester Evening News.
"We have lost the last two games so we have got to make sure we are back on top again and that means winning our games.
"If you put it into context then we have lost two games in four months.
"Overall that's not a bad record, but because the emphasis has been placed on the last two games, it looks very bad.
"So, we are not too worried, though we need to win the next game."