The German defender has been a regular fixture this season for Arsenal, featuring 40 times and scoring 3 goals, although some Gunners fans have questioned his performances as Arsenal have struggled to find any defensive consistency under Unai Emery.
Despite this, Mustafi will reportedly be in demand this summer, meaning his Arsenal future could now be in doubt.
In particular, the ex-Sampdoria defender is thought to be keen on a return to Italy to play in the Serie A - a league which he left five years ago as he joined La Liga side Valencia.
The 'Daily Express' report that the North London side would be willing to consider offers in excess of 20 million euros, with AC Milan believed to be looking for a centre-half to bolster their leaky defence.