It's still nowhere near a problem. Zinchenko is our undisputed left back, cancelo plays there as much as he does right back and ake and laporte will see game time there.
Bringing in somebody else limits playtime for 7 other players as all our defenders are impacted. Cancelo, laporte zinchenko and ake all directly get less game time, walker gets less because cancelo plays more at right back and Dias and stones get less because laporte and ake need more games at cb. we've seen first hand it's already hard for Pep to keep everybody happy. Signing a left back means selling at least 2/3 unhappy players and having to replace them too. It's not a problem at all.