Manchester United manager Ole Gunnar Solskjaer felt Fred's tackle that saw him sent off was "nowhere near a foul" but said the midfielder may have been lucky earlier.
Fred was sent off in the second half of United's 3-1 Champions League loss at home to Paris Saint-Germain on Wednesday.
The Brazilian was booked in the first half for an apparent headbutt on Leandro Paredes, before getting his second yellow card after appearing to win the ball ahead of Ander Herrera.
Fred conceded four fouls but his eight possessions gained were the equal most at Old Trafford despite seeing red with 20 minutes remaining.
Solskjaer lamented the decision that saw the midfielder sent off, although admitted he may have been fortunate earlier.
"We spoke to him at half-time – and be sensible – and I thought he was. I thought he played really well," he told a news conference.
"I thought he was very, very sensible in the second half and he covers the ground, he gets up to men without trying to tackle. The ball that he actually gets a yellow card for though, the tackle, that's nowhere near a foul. So, if you see that again, that's a mistake by the referee.
"But that's also human error, it's allowed. You can't, I can't sit there and complain about that now. I thought Fred was unlucky there, but he was probably lucky enough to come off for the first half."
Neymar's brace and Marquinhos' goal was enough to move PSG onto nine points, alongside United and RB Leipzig, in Group H.
Marcus Rashford had equalised for United in the first half, becoming the first player to score in all three home games for the club in a single group stage in the Champions League since Ruud van Nistelrooy in 2004-05.
Solskjaer was pleased with the forward, who has scored more goals in five Champions League games this season (six) than he managed in 18 appearances in the competition across his previous two campaigns.
"He's really taken to that role really well. And he's certainly giving us threat down the side, penetration, crosses, finishes. I've been very pleased with Marcus on there," he said.
"I know sometimes a right-footed striker would like to play on the left to come inside and score goals, but he's proving very efficient from the right side as well.
"And through the middle, he's played through the middle this season, as well, really well. So he's developing really well into the top forward for us."
Rashford was substituted with 16 minutes remaining and Solskjaer revealed the England international is struggling with a shoulder problem ahead of Saturday's Premier League trip to West Ham.
"It's just niggling him, that shoulder injury," Solskjaer told BT Sport. "Let's see how quickly he can recover. Let's hope he can be ready for the West Ham game. But we don't know."