Tottenham want to wrap up a deal with Sporting Lisbon for right-back Pedro Porro today amid fears Chelsea could hijack the move.
Spurs' £32.5m bid was knocked back but talks with the Portuguese side will resume on Wednesday morning over a revised structure of payments, plus bonuses and a possible player in return.
Porro, 23, is of interest to Todd Boehly's big-spending Blues, who are lurking if Tottenham's move breaks down, but the player's agent is focusing on Spurs first and seeing whether the clubs can agree a fee before discussing any alternative options.
Chelsea want a right back to provide cover for Reece James, and Tottenham - who themselves hijacked Everton's move for Villarreal winger Arnaut Danjuma - may fall victim to the same tactic if they are unable to agree terms with Sporting or Porro.
Spurs have made the Spanish star, who was at Manchester City between 2019 and 2022, their main target for this window, given Antonio Conte's side remain vulnerable at the back.
Sporting have been previously pointing to his buy-out clause of £40m, but it is understood there may be a softening in their stance if Tottenham can reach £30m plus bonuses.
Porro, who has also operated as a right wing-back for Sporting, has made 96 appearances for the club, scoring 12 goals and providing 20 assists.
Since Kieran Trippier left Spurs back in 2019, Spurs have been unable to find someone with the same quality at right back - with Emerson Royal and Matt Doherty failing to deliver at the moment, while youngster Djed Spence is barely featuring.
Meanwhile, at the other end of the pitch, Tottenham striker Harry Kane expects to hold contract talks over the coming months, but remains focused on trying to win his first trophy for the club.