Louis van Gaal branded Juan Mata's two quick-fire yellow cards against West Brom as "stupid" after he watched Manchester United slump to a 1-0 defeat at The Hawthorns.
The Spain international blocked Darren Fletcher's free-kick before tripping his former team-mate just three minutes later, earning his first Premier League dismissal in the first half on Sunday.
West Brom went on to seal the win through Salomon Rondon's strike and Van Gaal was left to rue Mata's recklessness – though he did question referee Mike Dean's readiness to issue the second booking.
"We've have played 60 minutes with 10 against 11 and this is the fifth match in 14 days, so it is very difficult," he told Sky Sports. "I think that's the reason we lost this game. We didn't give many chances away in the first half or the second half. The only chance more or less was the goal. It's a big pity.
"You can see the first yellow card is stupid. It's difficult, but I think the referee has to know the person who makes the tackle and Juan Mata never hurts an opponent. And it is his first [red card].
"You have to know all the characters, that's why an experienced referee is always better because he knows the players better, he knows the game better, and you take that into account."
With United now three points adrift of the top four, having played a game more than fourth-placed Manchester City, Van Gaal admitted that they could need to win all nine of their remaining fixtures in order to seal Champions League qualification.
"It's a big blow, you have to win these kinds of matches," he said. "We need 27 points. It's a lot, but it's always possible."
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