According to a news report, Rashford won't immediately be a key starter in the lineup. However, this doesn't mean his role isn't important. He will be a key player on the bench, available for various rotations.
Source: ansi Flick on Marcus Rashford As I thought before that Hansi Flick did not really want Rashford to fill the main player he was only used as a backup option when the main player could not play or was injured especially Lewandowski who was getting older of course he was more prone to injury so to avoid bad things Hansi Fluck borrowed Rashford from Manchester United, I have to admit this step was actually quite smart because Barcelona chose to borrow Rashford to see his abilities first before buying him permanently but I also felt sorry for Rashford after he found a gap to develop at another club but he was only used as a backup option.