Rashford joining Barcelona is going to affect some players in the squad, players like Dani Olmo and Fermin Lopez, this players play as a midfield and i believe Hansi flick will use Raphina in the midfield in some matches and Rashford to play as a winger, Rashford might not complain about the minutes he play but he will not like it when he is being benched more than 5 matches.
Dani Olmo and Fermin Lopez are star players and they will want to contribute to the team success and without not having much time to play they will feel like they are not important to the team, Rashford will be very important to Barcelona most especially when a player like Raphina or any attacking player gets injured but there is still going to be a problem, Rashford will also stop the way he play in Manchester United if not Barcelona will not have any intention of buying him permanently.
Raphinha as midfield? I don't think so, if Hansi Flick needed a midfielder he would've signed one instead of converting one of his best player that thrived in the left flank last season to the midfield and displace two other important players, makes no sense. If you have said he rotate between Raphinha and Rashford on the left flank then it's understandable but to play Raphinha out of position just to fix Rashford that was bought on loan is not a good idea, it seems you forgot that Raphinha is a very important player for Barcelona and his best position in that team is from the left flank, Flick won't take that risk of playing him in the Midfield.
First of all, we have to understand that Rashford has come to Barcelona on loan. He is not a permanent player in Barcelona's squad. Even after next season, there is no surity that Rashford will be in Barcelona's squad. So , will Hansi Flick change the position of his tested player Rafinha for Rashford? It is foolish to think that.
Last season , we saw Lewandowski, yamal and Raphinha perform excellently. Barcelona's defense was a bit weak , but their attack was very strong. FLick will not make any changes in this attack. Rashford will probably get a place in the squad as a substitute player or we will see Rashford in the squad after any player gets injured. Yamal and Raphinha are more important to Hansi FLick than Rashford.