Town have announced that goalkeeper-coach Jimmy Walker is leaving the club with immediate effect with Blues boss Paul Cook set to recruit a replacement.
In the meantime academy keeper-coach Carl Pentney will temporarily work with the club's first-team glovesmen.
"I have thanked Jimmy for his work at the club,” Cook told the club website. "I explained to him that I just want to look to freshen things up right across the board.
"Jimmy knows the game and change often happens in football when a new manager takes over. I want to wish him all the best for the future.
"Carl will work with the keepers for now and we will immediately begin the process of looking for the right person to come in and join the staff.”
Cook's Wigan goalkeeper-coach Nick Colgan, who had a brief spell with Town as a player without making a senior appearance, is currently working at Nottingham Forest.
Walker's departure leaves first-team coach Matt Gill as the only remaining member of Lambert's staff still at the club.
Cook brought in Gary Roberts as another first-team coach, while U23s coach Kieron Dyer has played an increasing role with the senior side since Cook took over, the new manager having been impressed by the former England international's coaching abilities.
Leam Richardson, Cook's assistant at Chesterfield, Portsmouth and Wigan, has been linked with a move to the Blues in the summer, however, appears increasingly likely to be offered the Wigan's manager's job. Richardson is currently interim-boss of the Latics.
We understand former Blues central defender John McGreal, who played alongside Cook at Tranmere, is also in contention for a role at Portman Road.
Walker joined the club in November 2018 following Paul Lambert’s appointment as manager having been working at Sunderland.
The 47-year-old had played for Lambert during a loan spell at Colchester United during 2008/09, making 16 appearances.
The Sutton-in-Ashfield-born keeper began his playing career at Notts County before a long spell with Walsall where he made his name - making 404 of his total of 483 league starts plus two sub appearances - and secured a Bosman free move to West Ham in the summer of 2004.
Having played for the Hammers in play-off semi-finals against the Blues in his first season at Upton Park, he joined Tottenham in September 2009, before returning to Walsall - where he added another 50 league starts - prior to stints with Peterborough and Lincoln.
Walker, who is based in Stamford, began his coaching career with Posh in 2013 before moving on to Gillingham and then the Imps during their 2016/17 Vanarama National League championship campaign, in which they beat the Blues in the FA Cup, before joining new Sunderland’s staff that summer.