The summer transfer window has been open for quite a while in England and it closes on 9 August - just before the new season kicks off.
Signing Fellaini is something Gunners fans likely wouldn't approve of, but on a free transfer, there's no real risk involved with the deal.
The Belgian international's representatives are all set to meet Arsenal officials to discuss a proposed switch this summer, despite an offer from his current employers which it seems he is unlikely to sign.
Fellaini, who made his name at Everton, is now away with Belgium's World Cup squad and is not expected to make any decisions over his future until he returns from Russian Federation next month.
Fellaini was signed by David Moyes as United looked to a new future following the end of the Alex Ferguson era at Old Trafford and now the same player could provide evidence of a changed approach at Arsenal following the exit of Arsene Wenger last month. He also wanted a significant pay-rise.
The 30-year-old moved to Old Trafford in 2013 and has struggled to fit in ever since, as David Moyes, Louis van Gaal and Mourinho asked him to play as more of a traditional central midfielder. The 30-year-old is now on £80,000 per week.