The 27-year-old started Napoli's 1-0 Europa League defeat to Arsenal on Thursday, and has been persistently linked with a move to Old Trafford.
But the Senegalese stopper has insisted he remains focused on the remainder of his season in Italy, rather than on a potential move away.
"I grew up in this league. It's the league that made me the player I am today," he said. "To me what matters most is to finish the season well, then we'll see."
Carlo Ancelotti also ruled out a transfer for Koulibaly, according to the Manchester Evening News.
"Koulibaly is the best centre-back in the world," said the Italian. "He is non-transferable. Napoli do not need to sell, the president does not want to sell and the question does not arise."
If Ole Gunnar Solksjaer and Manchester United can convince Napoli to sell, the 27-year-old won't come cheap.
The Italian side are expected to demand a fee in the region of £90m, which would break the current world record transfer fee for a defender set in 2018 by Liverpool when they bought Virgil van Dijk from Southampton for £75m.
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