I think that Sessegnon would play as an LW, or as a LWB in a 3-5-2. Don`t think he would be a LB in a 4atb formation
Sessegnon has played about 40% of his games as a LB this season, in a back 4.
He's certainly excelling at the LW role this season but remember he's 17, a lot of his problems defensively are physical and from a lack of experience. Pep would sort out his positioning quickly, he'd improve him as a defender, and time will take care of the physical side.
If a club got hold of him and wanted him to be a LB either full time or as a part time role playing on the wing on other occasions, they could definitely do it.
I think we can buy a lot better LW for the price but he is good young and Pep might be up for the challenge
What's special about Sessegnon in my opinion is his Sterling-esque ability to be in the right place at the right time. He anticipates things so well, he arrives in space so well, it's the main reason he scores so many goals. However, unlike Sterling (23 year old sterling) he has a variety of finishes, and better crossing. He takes people on in a way more similar to Sané, but he's more comfortable with his right foot than Sané.
If it sounds like I'm saying he's better than those two, I'm not, obviously they are playing at a much higher level and with much greater consistency, but Sessegnon has the ability to become a hybrid of the two, a real all-round winger.
I don't think we'll be interested in him though. We seem to be looking at players who'll make an impact in big games and improve our side immediately, which isn't a 17 year old.