Since his arrival from Torino in 2015, Darmian has failed to convince in the Premier League that he is capable of performing consistently at the high standard expected by Manchester United.
The 28-year-old only made 8 appearances last season in the English top flight, and, at this stage of his career, a move to secure more game time makes perfect sense.
His departure would however leave the Red Devils thin on the ground in terms of right-back options.
According to Mourinho, neither new signing Diogo Dalot or the veteran Antonio Valencia will be fit in time for the start of the Premier League campaign. In any case, they are aged 19 and 32 respectively, which raises questions about either of them being suitable first choice candidates this season.
If Darmian departs this summer, expect to see a new first choice right-back arrive at Old Trafford before the transfer window shuts.
Mourinho might want to consider making Santiago Arias that new signing.
Santiago Arias enjoyed a fine campaign with PSV in the Eredivisie last season. 3 goals and 6 assists from the right-back position are impressive figures, and defensively the 26-year-old was consistently solid.
This should come as no surprise, as the Colombian international has been reliably excellent for the Dutch giants since joining them in 2013.
Bigger things await for Arias though, and a switch to Old Trafford this summer would afford him the opportunity to prove that he has what it takes to make it at the highest level.
Transfermarkt value Arias at £16.2 million, but with the player entering the final year of his contract with PSV, he could be available at a bargain price.
Importing from the Eredivisie into the Premier League has proved a risky strategy in recent years, with more misses than hits in terms of players being able to make the step up. In this case though, this is a gamble worth taking for United.