The German defender has been the subject of plenty of criticism since joining from Valencia for £35million in 2016.
Former Gunners boss Unai Emery told Mustafi he could leave in the summer of 2019, but last season under Mikel Arteta, the centre-back was in resurgent form.
An untimely knee injury in the FA Cup semi-final win over Manchester City back in July halted his progress, and he has made just three appearances for the Gunners so far this campaign since staging his return.
However, Mustafi’s contract is due to expire next summer, and Arsenal hero Campbell can’t see the 28-year-old sticking around beyond then.
When asked whether the centre-back will leave the north London club at the end of the season, Campbell told Football Insider: ‘That is a done deal. I think it is a done deal from both sides.
‘Mustafi has taken a lot of stick in the past. It is difficult for players to take but we know what fans are like. If you make the mistake the fans will be on you but if you play well they will pat you on the back.
‘That is just the way high level football is right now. We have all suffered it.
‘If you have a bad game you can suddenly be the worst thing since slice bread. Mustafi has had a good run at Arsenal but it is definitely coming to an end.’
‘When I made a decision to sign for Arsenal it is because I respect this club,’ the defender said before the Gunners’ 3-0 victory over Dundalk in the Europa League last week.
‘It is a huge club, that’s why for me if I could stay at Arsenal, of course it would mean a lot to me.’