The figure was an add-on in the deal that saw the midfielder move to White Hart Lane for an initial £5m, the Mail explain, and will not be the last additional payment Spurs make should Alli continue to feature in Roy Hodgson's side in the future.
Given the way that the 19-year-old has started life as part of Mauricio Pochettino's side - having spent the second half of last season back on loan at Stadium:MK - it would certainly not be a surprise if Alli becomes a future talisman of the national side.
He already provided an indication of the player he could be when he scored a stunning effort past Spurs teammate Hugo Lloris to open the scoring when France travelled to Wembley for a friendly last week.
Despite beginning the campaign without an appearance for his club, Alli has established himself as one of the very first names on Pochettino's teamsheet.
And if he continues to progress at the rate he has done over the previous few months, then Spurs are likely to have absolutely no problems making further payments to the Championship side.