It would appear that Mourinho rates Tuanzebe but perhaps doesn't trust him to play central defence at this stage. 4 starts in the PL at the end of last season, 3 as a defensive midfielder, one exceptional performance as a right-back against Arsenal and 22 mins as a right-back against Wigan in the FA cup. This season, one start as part of a back three against Swansea in the League Cup and now 17 mins as a right-back.
Unlike McTominay, Axel has only been an unused sub twice this season, despite numerous injuries to central defenders and Lindelof's poor early form.
If there is a decent loan offer for the 2nd half of the season, I'd certainly consider it. Might change my mind if he starts against Bristol City in the League Cup and Derby in the FA cup.