Rhys Priestland will leave a big hole at Scarlets if the Wales fly-half goes, says former Wales and British and Irish Lions scrum-half Dwayne Peel.
Priestland, 27, is expected to announce this week he will join English side Bath after the 2015 World Cup.
Bristol scrum-half Peel opted to leave Scarlets for Sale Sharks in 2008.
"He'll have his reasons for doing what he's doing, but purely from Scarlets' point of view I'm sure they're bitterly disappointed," Peel, 33, said.
"He's very influential and we saw that when he played Saturday night for Scarlets against the Ospreys [in a 22-10 win].
"He was man of the match and he led the team, and to lose someone like that who's been there since he was a kid will be a massive loss for them."
Priestland is out of contract at the end of the season and has held talks with Scarlets about a new deal.
But Peel says that if Priestland's departure to the Recreation Ground is confirmed, he will be joining a club on the rise.
It is thought that South Africa Test number eight Duane Vermeulen is another key recruitment target.
"He's [Priestland] obviously happy with what Bath are offering him both on the field and off the field, and I'm sure he's excited about the move," Peel added.
"Bath are a massively ambitious club, you can see that in the signing of Burgess from the NRL, Matawalu is playing well in the Pro12.
"They've got a lot of money, a lot of investment going in there, fantastic training facilities and I'm sure they'll go from strength to strength."