Jay Rodriguez has returned to his home town club Burnley after the Clarets activited a clause in his contract.
The striker is believed to have agreed to add an agreement in his deal which would see him transferred for an initial £5m, plus a guaranteed £5m after 12 months, should Albion fail to win promotion.
Rodriguez had returned to pre-seaon training with the Baggies but Burnley were quick to snap up the 29-year-old, who came through their Academy.
Speaking in statement, Rodriguez said that he was "desparate" for Albion to get promoted back to the Premier League last season and that it had not been an easy decision to leave.
"At this stage in my career, I found the chance to play again in the Premier League at my hometown club too good to turn down and I hope everyone will respect that," he said.
“I have nothing but best wishes for the club I leave behind. I’ll be backing you to succeed in a new era under Slaven Bilić and hope that I can be back at The Hawthorns at the first available opportunity for a Premier League fixture.
“Until then, a sincere 'thank you' all for your support. I will never forget it.”