"I can't saying anything other than the deal for Vidic is 90 percent done," Indonesian Thohir told the website FcInterNews after arriving at Milan's Malpensa airport.
"When everything is sorted we will make an announcement."
Inter have been favourites to sign Serb central defender Vidic, who is out of contract with United at the end of the season, ever since the 32-year-old announced on Feb 7 that he would be leaving England at the end of the season.
Vidic joined United in 2006 and struck up a formidable defensive partnership with Rio Ferdinand. During eight years at Old Trafford he won a host of trophies, including five Premier League titles, the Champions League and the Club World Cup.
He came back from a serious knee injury to help United claim their 20th league title in Alex Ferguson's last season as manager, but has featured less this campaign thanks to further injuries and new boss David Moyes's desire to freshen up the side's defence.
Inter are fifth in Serie A and host struggling Cagliari on Sunday looking to close the 11-point gap separating them from third-placed Napoli who host Genoa on Monday.
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