Sky Sports understands that Tottenham are struggling to agree personal terms with Joao Moutinho having previously agreed a fee with Porto.
Spurs are prepared to break their transfer record to bring the Portugal international to White Hart Lane, with a £22m offer believed to be on the table.
Porto have sanctioned the sale of their highly-rated playmaker, who shone for his country at Euro 2012.
Tottenham need to move quickly, though, if they are to push an agreement through, with the summer transfer window set to slam shut at 11pm on Friday.
It appeared as though they would have plenty of time to bring Moutinho on board after being granted permission to talk to the player, but they have yet to reach an agreement.
Spurs boss Andre Villas-Boas will be eager for a compromise to be reached as he has seen his playmaking options severely depleted by the sales of Luka Modric and Rafael van der Vaart.
He knows Moutinho well from their time together at Porto and is well aware of what the talented 25-year-old could bring to his squad.