In terms of PL minutes so far this season:
Darlow (0')
Gillespie (0')
Karius (0')
Krafth (0')
Dummett (0')
Ritchie (0')
Lewis (7')
Manquillo (10')
Shelvey (34')
Anderson (96')
Lascelles (104')
Isak (244')
Wood (264')
Fraser (311')
Saint-Maximin (378')
Targett (421')
Murphy (484')
One of Darlow/Gillespie/Karius surely has to leave in January, even just on loan if it's Darlow/Gillespie, with Dummett and Ritchie in the same boat.
Lewis and Manquillo have contributed next to nothing this season and aren't good enough anyway, so I'd hope they could be sold if we manage to sign a young RB.
Anderson probably needs another loan, assuming Isak and ASM won't be so crocked for the rest of the season and with the hope we might sign another midfielder and/or forward player. If we get two in, then Fraser could definitely go as well.
Wouldn't be comfortable losing anyone else, really, but when we get to summer then Lascelles, Shelvey, Wood, ASM, Targett, and Murphy are probably going to be fair game for a move.
Based on minutes, our first XI this season has been:
Pope
Trippier Schär Botman Burn
Longstaff Guimarães Willock
Almirón Wilson Joelinton
Howe the fuck are we third?