Director of performance Dr Mark Gillett, who was known simply as the ‘Doc’ at the Baggies, headed up a team of six people.
The former Chelsea first-team doctor arrived at the club in 2010 as head of sports science and medicine before becoming director of performance five years ago.
But he has now resigned to take up a new role with Championship rivals Forest.
“The club has been a huge part of my life,” Gillett told the Express & Star.
“It wasn’t an easy decision to leave, but after eight years I needed a new challenge and wanted to tackle something with renewed energy. It was a tough season for everybody.”
Gillett’s team were named the Premier League’s medical and science team of the year in the 2016/17 season after keeping the majority of Albion’s players fighting fit for that campaign that saw them finish in the top half under Tony Pulis.
Albion are now on the hunt for a replacement, adding a further appointment due to be made this summer.
Since the season has finished, Darren Moore has been installed as head coach and Li Piyue has been named club chairman.
Moore is closing in on a new assistant, but an appointment is not expected until later on this week at the earliest with an announcement next week most likely.
Albion’s head coach has also been speaking with his players ahead of next season, in an attempt to convince as many as possible to stay and fight in the Championship.
He’s visited as many as possible in person, such as England stand-by Jake Livermore, who has remained in the country to train ahead of the World Cup, and has spoken to others who are on international duty or away on holiday on the phone.
“At the moment I’m speaking to them all individually,” said Moore. “There’s a transfer window, it’s going to be a busy one.
“They’re all contracted to the club, they’re all good players. We want to keep our good players in the building and we’ll be doing everything we can to keep them.
“As for an exact number (who will stay), I can’t give that now.”