Centre Back 1: Chris Smalling vs Gerard Pique
Chris Smalling has had an inconsistent, injury-prone career at Manchester United, but like Pogba and Lukaku, has responded positively to Ole Gunnar Solskjaer's arrival to Old Trafford. He has been a defensive mainstay since, putting in stellar performances against Paris Saint-Germain and Liverpool recently. He has also benefitted from the fact that Solskjaer often resorts to 3 man centre back system against big teams.
World Cup winner Gerard Pique, on the other hand, is having a beast of a form since the last few games. The lack of a regular defensive partner may be the problem, with Valverde trying out Clement Lenglet and Thomas Vermaelen in that position given the injury layoff of Samuel Umtiti. Lenglet has put in some solid displays off late and it should be the Pique-Lenglet combination that takes the field against United.
Verdict: For the sake of statistics, Smalling has an edge with better tackles, clearances and blocks per game and fewer occasions where he has been dribbled past. He is even better if Soskjaer decided to play a 3 man central defence against Barcelona. Pique, on the other hand, is a brilliant distributor who furthermore offers an offensive threat, and has already scored 7 goals this season.
He is more dominant in the air and is less prone to giving away fouls and the lower count in terms of clearances and blocks can be attributed to Barcelona dominating the possession in most of their games.