According to Miguel Delaney of The Independent, the Red Devils want to take advantage of the German's current contract situation, with his deal at the Emirates Stadium set to expire at the end of the campaign. It means he can discuss a deal with other clubs in 2018 with a view to moving in the summer.
Another Arsenal star, Alexis Sanchez, has a contract situation similar to that of Ozil, and the Red Devils have an interest in him too, even if Manchester City are the favourites to land the Chilean at this point, per Delaney.
As noted by Daniel Storey of Football365, the two attackers have been vital to the Arsenal cause ever since they first linked up together at the Emirates Stadium:
Daniel Storey @danielstorey85
Since Alexis Sanchez joined Arsenal, they have never won a Premier League game in which neither him nor Mesut Ozil started.2017-9-17 11:59:37
Ozil joined from Real Madrid in 2013 for a then-club-record transfer fee of £42 million. In that time, he's had some wonderful moments in an Arsenal shirt, though for all his technical quality and passing ability, he has split opinion.
One school of thought will say Ozil is among the finest No. 10s in the game if he's given freedom and is surrounded by capable footballers; others view him as a luxury and will point to a string of poor performances turned in by the 28-year-old in big games since he arrived at Arsenal.
Per Martin Laurence of WhoScored.com, there is a tendency to make Ozil a scapegoat at times:
Martin Laurence @martinlaurence7
Must be difficult being Mesut Ozil. He's at fault for everything ever, isn't he?2017-9-19 13:23:23
As noted by Delaney, the Red Devils boss wrote the foreword for Ozil in his autobiography and "Mourinho is highly confident of convincing him to join United based on their previous working relationship at Real Madrid."
With so many other combative players in his United team, perhaps Mourinho feels he can find a role that would see the German flourish in a way he hasn't at Arsenal.
Bleacher Report's Dean Jones recently gave an insight into the relationship between the two men:
B/R Football @brfootball
Could Mesut Ozil really join Manchester United? @DeanJonesBR separates the fact from the fiction | https://t.co/xrvwf1wVNJ https://t.co/LB95Q3FNnA2017-9-20 14:24:01
For Arsenal supporters, losing Ozil and Sanchez on free transfers would be disappointing next summer. Though there's little the club can do at this point, there will be questions asked as to how this situation has come to be, with plenty no doubt of the opinion the club should have cashed in while they could.
If United did move for him, you sense Ozil would be keen to work under Mourinho again and join a club that looks closer to challenging for major honours than the one he is at.