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Inter Milan have turned down a £57m ($81m) bid from an unnamed club for 22-year-old centre-back Milan Skriniar, his agent has claimed.
Karol Csonto said Barcelona, Manchester City, Manchester United and Real Madrid had all expressed interest in signing Skriniar, who joined Inter from Sampdoria last summer.
The Slovakia international has played every single minute of Inter's Serie A campaign thus far, scoring three goals.
Csonto ruled out a January move for Skriniar as Inter do not want to lose the defender midway through the season, but said his client could change clubs in the summer.
"I knew he would never leave in this window, but I can confirm that big clubs like Barcelona, Real Madrid and the two Manchester clubs are interested," the agent was quoted as saying by the Sun.
"And I can also add that one of these clubs has made a £57m bid for him. Inter rejected it, telling me that they can't afford to lose their defender now.
"I can't really say [whether Skriniar could move in the summer], but there are still a lot of months and a lot can happen."
Barcelona signed Palmeiras centre-back Yerry Mina for £10.4m earlier this month, while Manchester City signed French defender Aymeric Laporte from Athletic Bilbao for a club record fee of £57m this week.
Spanish daily AS reported that Inter will only sanction the sale of Skriniar in the summer if they can persuade Atletico Madrid defender Diego Godin to move to the San Siro as his replacement.
Meanwhile, Inter have been linked with deadline day moves for Paris Saint-Germain forward Javier Pastore and Atletico winger Nicolas Gaitan.
Nerazzurri coach Luciano Spalletti is reported to have blocked Marcelo Brozovic's loan move to Sevilla until the club can sign a suitable replacement.
Inter are on a seven-game winless run in all competitions and are 13 points behind Serie A leaders Napoli in fourth place.