According to Gazzetta dello Sport (h/t Harry Slavin for MailOnline), the Serie A side value the 23-year-old highly and would not sell even for £65 million.
Inter are in talks to extend Skriniar's deal, which expires in 2022, but are yet to reach an agreement, which has alerted the Red Devils and Manchester City, per Slavin.
Skriniar has developed into one of Serie A's most impressive defenders since moving to the San Siro from Sampdoria in summer 2017.
Scouted Football highlighted his record since joining the Nerazzurri:
The Slovakia international looks to have his best years still ahead of him. Football commentator Matteo Bonetti explained why he's so good:
Manchester United have struggled defensively this season, and manager Jose Mourinho is yet to find a settled centre-back pairing.
Rob Dawson of ESPN FC noted how superior their defensive record was last season:
The club were linked with a number of defenders over the summer but failed to bring in any reinforcements at centre-back.
Toby Alderweireld, Harry Maguire, Yerry Mina and Jerome Boateng were all targets for the Red Devils, according to Jack Otway at the Daily Express.
Ciaran Kelly of the Manchester Evening News said the Red Devils still need defensive recruits:
Ciaran Kelly @MENCKelly
@ManUtdn63836693 In the transfer market? I still think a quality centre-back and a back-up striker are needed in January. On the field, Mourinho needs to be more proactive. Three at the back and Scott McTominay in defence vs West Ham?! Have to start games like those comebacks.
Skriniar has spoken about rumoured interest from Manchester United but said he did not know if there was any truth in the speculation.
"Personally, I don't know, as the transfer window has just shut, so it's hard for me to say anything," he told Sport.sk (h/t Metro). "There was some noise in the summer, but nothing happened, so I'm not letting it bother me."
Strengthening the defence looks to be a priority for Manchester United after a tough start to the season. The team have conceded 16 goals in nine league matches; only Burnley, Huddersfield, Cardiff City and Fulham have let in more.
However, trying to prise Skriniar away from Inter looks a tough ask. The club will not want to lose one of their key assets, and it remains to be seen if Manchester United are willing to invest so heavily in the January window.