The 27-year-old has been at the club for five and a half years and was the longest serving player having gone through promotion and the FA Cup agony as well as winning Hammer of the year in his first season after joining from Spurs.
Etherington has been allowed to leave the Boleyn as Gianfranco Zola looks to offload fringe players in order to keep his star players from the clutches of mega-bids coming in.
The manager said to the official site, "It was the best deal for everyone. He is going to be playing regularly. We left on very good terms and we wish him all the best."