Manchester United manager Ole Gunnar Solskjaer felt the inexperience of the referee cost his side a result away to Young Boys.
The Premier League big-spenders were beaten 2-1 away to the Swiss champions in their opening Champions League Group F encounter.
United took the lead on 13-minutes when Cristiano Ronaldo did enough to beat Young Boys goalkeeper David von Ballmoos.
But their efforts were hampered by the sending off, ten-minutes before the break, of Aaron Wan-Bissaka.
The full-back was shown a straight red by referee Francois Letexier for a dangerous challenge on Young Boys midfielder, Christopher Martins.
"Well, I can understand why he gives it because Aaron takes a touch that goes too far," Solskjaer said, "It's never a dangerous tackle, because he hits him on the front of his foot.
"We've seen sometimes... we saw Harvey Elliott, sometimes you can see bad injuries. It was never reckless or malicious.
"But probably a little bit [of] inexperience to go through there, after having the ball. But the boy wasn't going to be injured.
"And it makes it difficult after that, with ten men."
Solskjaer felt the referee denied United a penalty when Ronaldo went to ground in the hosts' box following the close attention of Mohamed Camara.
The United boss said, "Yeah, he shoves him with his arm, and it's a clear... he's one-on-one with the keeper. He's in front of him.
"But probably didn't dare do it [award a penalty], because he had to send him off then, so it would have been difficult.
"That's what sometimes you get with young referees."
While 32-year old Letexier has youth on his side, the French official has been a FIFA referee since 2017.
Solksjaer has drawn criticism for his game management following the defeat, but defended taking off Ronaldo and Bruno Fernandes when the score was still level.
"The game had gone 70-odd minutes, they'd been running a lot both Saturday and today," the Norwegian said.
"The astro-turf of course takes its toll as well, and we wanted Nemanja's experience [to] keep hold of the ball and Jesse's legs."
Solskjaer believes his side will learn from the defeat, particularly Jesse Lingard whose wayward back-pass allowed Jordan Siebatcheu to net the winner in the fifth minute of added time.
"That's football for you at the highest level," the United boss said, "Lack of concentration, make a mistake, and you get punished. You get done.
"We did that last year in Europe - we conceded a very, very, very sloppy - or two - counter-attacks against [Istanbul] Basaksehir, and we lost that game.
"Today, in the last seconds, Jesse just wants to play it safe. One mis-placed pass, and you've conceded a goal. And that happens in football."
Manchester United Player Ratings | Solskjaer’s men suffer embarrassing defeat to Young Boys
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