West Brom have confirmed they are in discussions with Derby over the possible sale of George Thorne.
Albion are due to fly out to America on Thursday for a pre-season training camp in California, but Thorne will remain in the Midlands while talks between the two clubs take place.
If a deal can not be agreed then the midfielder will link up with the rest of Alan Irvine's squad at a later date.
"The club are in talks with Derby about George and while those negotiations continue it makes sense for him to remain at home," West Brom boss Irvine told the club's official website.
"However, if no agreement is reached, George will be flown out to join the rest of the group in the US."
Thorne, who signed an improved three-and-a-half-year contract with Albion in January, enjoyed a successful four-month loan spell with Derby last season, helping Steve McClaren's men to reach the Sky Bet Championship play-off final at Wembley.
Those performances have seen the Rams table two bids for the 21-year-old which were both rejected by West Brom.
Since returning to The Hawthorns, Thorne has spoken of his desire to join Derby on a permanent basis and he has handed in two transfer requests - which were also turned down by the club.
Meanwhile, Stephane Sessegnon will also be absent from the 23-man squad that travels to America as he has been selected for international duty by Benin for Sunday's African Nations Cup qualifier against Malawi.
West Brom will play two friendly matches against Sacramento Republic during their 11-day trip. They will take place at Bonney Field on July 21 and July 25.