Glamorgan all-rounder Jim Allenby is poised to join Somerset a little more than a year after signing a four-year contract.
Australian-born Allenby, 32, is likely to link-up with his former Glamorgan coach Matthew Maynard who is director of cricket at Taunton.
Former England batsman Maynard signed Allenby for the Welsh county in 2009.
Allenby scored 923 championship runs and took 52 wickets for Glamorgan in 2014.
Former Glamorgan and Sussex batsman Tony Cottey, said the move would leave Glamorgan with "a massive hole to fill" in their squad.
"He's been a fine player for Glamorgan since he moved over from Leicestershire - in both one-day cricket and the championship," said Cottey.
"They're going to miss his runs at the top of the order in T20, where he had a great opening partnership with Jacques Rudolph.
"But as an all-round cricketer he was a fine first-change bowler as well, with vital wickets in the championship. It's a massive hole to fill."
Cottey believes it will be difficult for Glamorgan to find the right replacement.
"Usually when people commit to three or four years (on a contract) you build your side around them," he added.
"How do they replace like-for-like? There aren't many players like Jim Allenby on the market and lots of counties would be in a queue for them."
Glamorgan have only so far announced the recruitment of Northamptonshire opening batsman James Kettleborough, but more signings are expected despite the county's focus on developing home-grown talent.
BBC Wales Sport understands that Glamorgan are negotiating with Somerset about a possible loan deal for their 22-year-old all rounder, Craig Meschede.