Critically, Chelsea lacks a direct winger.
Staleness in attack seems to be Chelsea’s biggest issue this season, and while part of the issue is an overly defensive formation, it's also partly because Eden Hazard is Chelsea’s only performing inside-forward. Pedro has been involved in just five goals from 16 league matches so far this season.
Antonio Conte could do with a different sort of player to complement Hazard, perhaps a more direct converted winger to break the lines and run in behind Alvaro Morata.
And the only player that could fit in that position and fit in that style of play is Crystal Palace's Wilfred Zaha