The ESPN FC reporter believes the Italy international could leave the Europa League winners in the 2017 summer transfer window.
Juventus are expected to lose Brazil internationals Dani Alves and Alex Sandro this summer, with both full-backs heading to the Premier League.
Darmian has been touted as a potential replacement should Alves or Sandro leave the Champions League runners-up.
The 27-year-old made 18 appearances in the Premier League last season as Darmian was in and out of the first-team under Mourinho.
Serie A expert Amoyal believes Darmian could seal a return to Serie A summer if Manchester United receive a suitable offer for the former Torino star.
“With Dani Alves set to join Manchester City and Chelsea pushing to sign Alex Sandro, Juventus are focused on adding one or two wing-backs,” Amoyal wrote in his ESPN column.
“Darmian could be returning to Serie A since Jose Mourinho appears open to letting him leave for the right offer.
“Considering that Juventus have just one non-EU slot available and are pushing to sign Douglas Costa, acquiring the Italian defender rather than Real Madrid’s Danilo would leave give them more flexibility when it comes to bolstering other positions.”
Manchester United were 3-2 winners against Southampton in the EFL Cup final at Wembley back in February.
The Red Devils secured their place in the Champions League next term thanks to a 2-0 victory over Eredivisie giants Ajax in the Europa League showpiece.
Mourinho has only signed Victor Lindelof in the summer transfer window so far.
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