Southampton have asked the Premier League to investigate an alleged illegal approach from Liverpool for Virgil van Dijk, Sky sources understand.
A source at St Mary's has told Sky Sports News HQ that, although the club has concluded a number of transfers with Liverpool in recent years, they feel the Reds have overstepped the mark in trying to convince Van Dijk to move.
The Premier League later confirmed they will look into the matter, with a spokesman stating: "Southampton have raised some concerns and we are in turn raising them with Liverpool."
Van Dijk is understood to favour a move to Anfield over Chelsea and Manchester City but Sky sources are adamant the player is not for sale and that any transfer fees - reportedly up to £60m with £200k-a-week wages on the table - are fantasy.
Southampton are determined to keep the Netherlands international and the player still has five years left on his current contract.
Southampton insisted on Tuesday that they have not yet had any official bids for any of their players, including left-back Ryan Bertrand, who is a target for Manchester City.
Sky sources understand Liverpool are prepared to break their transfer record - currently the £35m they paid for Andy Carroll in 2011 - and match any bid from Chelsea or City to land Van Dijk.
Sources indicate Van Dijk has been impressed with manager Jurgen Klopp's personal involvement in Liverpool's effort to sign him, but Sky Sports News HQ understands that personal terms with the player have not been finalised.
Sky in Italy reported on Monday that Klopp met with another of their principle transfer targets - Roma's Mohamed Salah - to agree personal terms over the last few days, as the clubs continue to talk over a potential deal.
Liverpool have so far signed one player already this summer - the soon-to-be ex-Chelsea striker Dominic Solanke - who will join when his Blues contract expires for a fee to be set by tribunal and expected at around £3m.