The Nerazzurri have bolstered their full-back options by bringing in the Portuguese on an initial loan deal
Cedric Soares has joined Inter from Southampton on loan until the end of the season.
The full-back secured his move on Saturday after arriving in Milan to complete a medical 24 hours earlier.
Inter have the option to sign the 27-year-old on a permanent deal, with the fee reportedly set at €11 million (£9.5m/$12m).
Head coach Luciano Spalletti had been keen to bolster his options at full-back, with Sime Vrsaljko struggling due to a knee problem since joining on loan from Atletico Madrid last July.
Manchester United defenders Matteo Darmian and Antonio Valencia have each been linked with a possible move to San Siro.
Cedric, a Euro 2016 winner with Portugal, made 119 appearances for Southampton in all competitions after arriving from Sporting CP in 2015.
The Nerazzurri are next in action against Torino on Sunday, before a Coppa Italia quarter-final meeting with Lazio on January 31.
Southampton, meanwhile, appear likely to continue to put faith in 19-year-old French defender Yan Valery in the right wing-back role.
He only made his Premier League debut for the club in the 2-2 draw with United but has appeared in eight games since then, including the 2-1 victory over Everton last time out.
Next up for the Saints is a league clash with Crystal Palace, with Hasenhuttl's side not playing this weekend having been knocked out of the FA Cup at the third-round stage by Derby County.