McTominay started the game in central midfield and put in a decent shift for his side.
United were well in the game until Marquinhos gave PSG a 2-1 lead against the run of play, before Fred got a second yellow minutes later.
Then PSG had control of the tie, and eventually scored a third on the break through Neymar, who also got their first goal.
Marcus Rashford scored United's only goal of the game.
"I'm hearing their goal was partly offside as well. For us where is the balance in the game with how the referee has approached decisions?" McTominay told BT Sport after the game.
"We're seeing mistakes week in, week out, for us it has to be rectified, get football back to the way it was (before VAR)."