Lyon has tons of high potential players, and while I'm a fan of Aouar and Tousart if we're signing one of them (aside from the obvious first choice Fekir) I'd pick Ndombele.
Still a bit raw but has all the tools to become a mainstay for the next 10-15 years in midfield, strong like an ox but moves in tight spaces like Cazorla. Think Vieira in terms of combining physicality with technique but remove height and add lots of pace, he's virtually unique as a player type, think Essien at Lyon maybe at a stretch. Can pick a defence splitting pass on the floor from between the centre halves, relishes a physical duel and as busy as Ngolo Kante on the pitch for 90 minutes, honestly I'd make him top priority for the summer and figure out what to do with the rest of our sorry ass midfielders afterwards
e: hah well done Ray, your post wasn't there when I started typing.