Manchester United and Tottenham are around £20 million apart in their valuations of Toby Alderweireld, sources have told ESPN FC.
United had hoped to tie up a deal for the defender before the start of the World Cup after securing early agreements with Shakhtar Donetsk and Porto for Fred and Diogo Dalot.
However, the Belgium squad, which also includes Romelu Lukaku and Marouane Fellaini, left Brussels for Moscow on Friday morning with United and Tottenham yet to agree a fee.
Sources have told ESPN FC that United are willing to pay around £50m for Alderweireld, but negotiations have hit a sticking point with Tottenham valuing the 29-year-old at closer to £70m.
The sources added that Tottenham are resigned to losing Alderweireld this summer after failing to agree the terms of a new contract. The centre-back has two years left on his existing deal worth around £50,000-a-week, which also includes a clause allowing him to leave for £25m next summer if he has still not reached an agreement with Spurs.
United are hoping to reach a compromise although sources have told ESPN FC that Tottenham are not willing to strengthen a direct rival without driving a hard bargain.
They point to Virgil van Dijk's £75m transfer from Southampton to Liverpool in January as the going rate for a top-class centre-half who is already proven in the Premier League.
United, meanwhile, are willing to look elsewhere if they cannot reach an agreement. Sevilla's Clement Lenglet is an option after he impressed Jose Mourinho during United's Champions League defeat to the Spanish side last season, and sources said that the 22-year-old Frenchman would likely cost considerably less than Alderweireld.
Mourinho is also an admirer of Raphael Varane, after the pair worked together at Real Madrid, and Jerome Boateng, whose future at Bayern Munich has been the subject of speculation in Germany since the end of the season.