The highly-rated midfielder saw out the 2013/14 campaign on loan at the iPro Stadium, helping Derby to the Sky Bet Championship play-off final.
He has expressed a desire to secure a permanent switch this summer, with one transfer request already knocked back.
Two offers for his services have also been rebuffed by West Brom, as they open a new era under the guidance of Alan Irvine.
Thorne’s future remains up in the air then, with Derby expected to return with another bid and West Brom still hoping that they can convince the 21-year-old to stay put.
Albion’s technical director Terry Burton said in the Birmingham Mail: “He’s an Albion player, he’s under contract.
“We think he’s a good player and we want to give him an opportunity to play first-team football, but ultimately that’s up to George.
“If George is the best man for the job then he will get into the team. We don’t have any favourites or any reason not to play the best person.
“I’m sure George will come back (for pre-season training) with the right attitude. And I’m sure he wants to play Premier League football, not Championship football.
“If he does, well then that platform is here. It’s in his hands.”