Bournemouth assistant boss Peter Grant is set to replace Paul Goddard as number two to Alan Pardew at West Ham.
Goddard (right) has been replaced by Grant at Upton Park
Grant played under Pardew at Reading before he became player-coach at Dean Court in the summer of 2000.
The ex-Celtic skipper was approached earlier this week, and admitted that it was an offer he could not refuse.
"I've had a great time at Bournemouth and the learning experience I've had is nothing short of phenomenal," he told BBC Radio Solent.
"But you want to play in the biggest arena with the best players - you want to try and improve your career all the time."
The 38-year-old made 470 senior appearances for Celtic before spells with Norwich and Reading, and won two full caps for Scotland in 1989.
Grant steps into the role vacated on Tuesday when Pardew decided to let Goddard go.
The former Hammers striker was appointed when Glenn Roeder became manager in May 2001, but Pardew admitted he was keen to bring in a new man.
"Paul has been totally professional but I just felt the chemistry needed to change.
"I have decided to bring in a new coach," he told the club's official website.
West Ham are currently eighth in Division One, four points off the play-off places.