United have got decent defenders like Eric Bailly and Victor Lindelof, who is another player that has been impressive under Solskjaer, but both of them would be better alongside a really commanding centre-half.
After a goalless first-half, Presnel Kimpembe converted Angel Di Maria's corner kick to give the visitors the lead in the 53rd minute.
'Of course, Neymar is super-important and Cavani is fundamental, but football gets played on the pitch. However, the tempo of their play dropped significantly following the restart and they were deservedly punished.
Marquinhos' versatility, which enables him to play in midfield or in the heart of defence, may come in handy for the second leg as the Parisians may look to sit deep and frustrate Manchester United at the Parc des Princes. This considered, United's frustration that the referee then chose to send Paul Pogba off (he'll now miss the return in Paris) for a second bookable offence in the closing stages was obvious.
The surf was definitely up for one steward at Old Trafford during Tuesday night's Champions League game.
"If you tease him then it does not make him weaker", said his manager Thomas Tuchel.
Ahead of the match, at the Radisson Blue hotel in Manchester, Tuchel was chilled, as though he had everything under control despite the enormity of the task ahead. He was right. The players never doubted themselves - but the media and the public did, creating a perception that United had become invincible and would overrun a weakened PSG.
United have already been outclassed at home by one of the best teams in Europe this season when Juventus beat them 1-0 in the group stages. "To defend like that and not allow chances". "It will be hard and it's a mountain to climb but it's not impossible". "That's a big blow because he's been fantastic for us". "We're Man United, we always bounce back".