Rashford really needs to work hard to avoid being benched; if he does not work hard, he won’t be among important players for the Barcelona squad, and that will affect him seriously, so I think he needs to work on that. Although he is a talented player and will want to be at his best performance, so he won’t want to miss any single opportunity given to him to do his best. So I’m sure Rashford won’t want a challenging playing for Barcelona. Barcelona had a successful season last season. I’m expecting Rashford to do well; Flick is going to do his best.
If he wants playing time, Rashford needs to work hard because if his performances aren't consistent, it will be difficult to earn Flick's trust. Barcelona has a number of quality players in that position, and it won't be easy for Rashford to get regular playing time. Rashford has great talent, but his ego is too big, which means not all coaches like his style and style of play. If this can be addressed, I'm sure Rashford will return to his best form at Barcelona over time with consistent training.