Isn't Grimaldo the obvious guy? 12 league assists last year and on pace for 9 if we'd had a full season. 24 years old, at a club who sells for money and presumably good enough to contribute offensively when we play Shaw at LCB in a 5 man defense and we desperately need attacking play at LWB since Wan-Bissaka is a uh, work in progress on the other side (low key bet is that Dalot comes good and becomes our first choice option in that role).
The other thing I could see is if we can't get Sancho this summer (or at all) is doing what Mourinho wanted when he was after Perisic, which is to say signing a left-footed winger with some defensive game like McNeil from Burnley or even better Saka from Arsenal if he wants the move and we offer Arteta money he needs to rebuild his side, and we get that player to play LWB and hopefully be our starting RW for a year then backup Sancho, though maybe we like Chong for that second role long-term...But if we give Greenwood the backup 9 job proper (along with say Ighalo for another year as a safety blanket) it might make sense. Let's say Pogba leaves and we spend big on 2 replacement mids and with no Sancho somewhat surprisingly buy a CB, plugging in some realistic but optimistic names:
-------------Martial--------- (Greenwood, Ighalo)
Rashford--------McNeil (James, Greenwood, Chong)
-------------Bruno---------- (Grealish)
-------Fred---Partey--------- (McTominay, Matic)
Shaw------------------AWB-- (Williams, Dalot)
--Upamecano-Maguire-- (Lindelof, Bailly, Tuanzebe)
------------De Gea-------------- (Romero)
or 3/5 at the back:
--Rashford----------------Martial--------- (Greenwood, James, Ighalo)
-------------------Bruno---------------------- (Grealish)
---------------Fred---Partey---------------- (McTominay, Matic)
McNeil---------------------------------AWB-- (Williams, Dalot)
----Shaw-Upamecano-Maguire-- (Lindelof, Bailly, Tuanzebe)
-------------------De Gea-------------- (Romero)
And then if McNeil isn't a star we still have a proper 2nd RW and a wingback who can cross, always useful.