If according that news report true I think bad decision for Marcus Rashford leaving Manchester United but for joining Barcelona but can't guarantee with regular or starting line up position. Actually Rashford can play well for several position as left, right winger side and central forward but recently the right winger have secured by Lamine Yamal, impossible for Rashford can fill at right winger side. The same at left side have been filled well by Raphinha scoring many goals last season and how possibility put Raphinha at the bench for giving early minutes playing to Rashford.
Possibility rotation seems at central forward for Robert Lewandowski's position, its depend his performance inconsistency or not, however Hansi Flick know well with player needed and rotation most important how to keep their players from injury and not huge difference level between main player with substitutes players.