Brentford drew 0-0 with Dynamo Kiev in a pre-season friendly in Austria after Neal Maupay was withdrawn from the squad.
Sheffield United want the Bees striker and there have been enquiries from Aston Villa, West Ham and Brighton.
West London Sport revealed on Saturday morning that Maupay had been granted time off by the club and would not feature in Saturday’s game.
Maupay, 22, is expected to return to his native France until early next week. He has been told to report back for training on Tuesday.
Brentford want at least £20m for Maupay, who scored 28 goals for them last season.
The Bees have noted that financially troubled Birmingham City sold striker Che Adams to Southampton for a reported £15m.
Brentford, on the other hand, do not need to sell so feel they can hold out for significantly more than that amount.
They have already banked sizeable transfer fees for several players in recent years, including the recent sale of goalkeeper Daniel Bentley to Bristol City and Chris Mepham’s January move to Bournemouth, so are in a position to play hardball.
There is also a belief that Maupay’s market value will increase further by the time the January transfer window opens if he stays at Brentford and continues his prolific form during the first half of the coming season.
Maupay was signed from St Etienne in 2017 and is under contract at Griffin Park until 2021.
The club’s preparations for the coming season continued with a stalemate in which Emiliano Marcondes had a first-half penalty saved after Ollie Watkins had been fouled in the box.