He wasn't due to play - I don't think there is long-term plan to play him on the right but Pepe pulling out (nine months too late it would seem). Better to stick Saka there then completely change the line up completely move our best player from his position (nominallly on the left) and leave the new full back with less cover - unless you think Auba does as much work as Saka defensively. Also if you want to bring stats into it - his normal shooting accuracy is 30% on the left 100% on the right - that proves he is more effective on the right then does it? I prefer him on the left though