Jose Mourinho bemoaned a "clear offside" goal after Manchester United's Europa League campaign got off to a losing start against Feyenoord on Thursday night.
Tonny Vilhena powered home the winner on 79 minutes, but Nicolai Jorgensen appeared to be in an offside position as he broke down the wing before crossing to set up the only goal of the game.
Manchester United were lacklustre going forward, but Mourinho insisted his side did not deserve to lose as the visitors suffered their second defeat in five days.
"Of course I'm not happy with the start," Mourinho is quoted as saying by the club's official website. "I think in the second half of the game, in my opinion, we were always in control.
"We were trying to win and they were trying not to lose. We felt like they were collapsing a bit physically, they were in trouble and it was that moment in which we lost the game. It was double unlucky because it was a clear offside [for Feyenoord's goal]."
Mourinho made eight changes from the side which lost the Manchester derby on Saturday, but the former Chelsea boss did not want to discuss individual performances or comment on whether those players given their chance had passed it up in the defeat.
"Look I don't want to personalise," he added. "Some of the players were playing their first minutes of the season, not many minutes for them.
"Obviously some played better than others but I have to understand that some of these players haven't played week after week like the other boys. "
Manchester United's next match is against Watford in the Premier League on Sunday.