Can Eric Bailly take the lead in central defence? Like him, the other players in his position at Manchester United all have their own significant challenges, but he seems to be by far the most talented of the pack.
Like Bailly, Phil Jones struggles with injury. Chris Smalling is fairly solid, with the occasional glaring error, but his greatest shortcomings are arguably in attack rather than defence -- more on that later. Marcos Rojo has enjoyed periods of good form, and plays the ball out well from the back, but there is a long-term question over his reliability.