Southampton have asked the Premier League to investigate an alleged illegal approach from Liverpool for Virgil van Dijk, after the Dutch defender made it clear he had spoken to the Anfield club.

Southampton are yet to receive any official contact from Liverpool regarding Van Dijk, despite the defender indicating he is eager to move to Anfield and reports of a fruitful conversation with Liverpool boss Jurgen Klopp.

Klopp is understood to have made Van Dijk his top target this summer and the chance to work with Klopp is believed to have been a significant factor in Van Dijk's decision.

But Saints have been irritated by what they see as an attempt to unsettle their player and are ready to reject an official offer, potentially reopening the door for Chelsea and Manchester City.

The Premier League rules state: "a club intending to conclude a contract with a progessional must inform the player's current club in writing before entering into negotiations with him. A professional shall only be free to conclude a contract with another club if his contract with his present club has expired or is due to expire within six months. Any breach of this provision shall be subject to appropriate sanctions."

Liverpool may now face an ever-tougher battle to secure the 25-year-old, who has become one of the most sought-after defenders in the league since moving to the south coast from Celtic less than two years ago.

Last month, Southampton chairman Ralph Krueger told Press Association Sport the club could turn down even a £60m bid for Van Dijk.

"Can we? Yes," Krueger said. "We do not need to sell any player for the first time since I've been here."

Van Dijk signed a six-year contract 11 months ago but made only 21 Premier League appearances last term after missing the second half of the season with an ankle ligament injury.