Webster has been on Town's coaching staff for a number of years, having worked with such keepers as Richard Wright, Andy Marshall as well as current Number One Kelvin Davis.
With Webster leaving the club Town boss Joe Royle has decided to bring in Andy Rhodes to work with the goalkeepers at the club, but has stressed that this is only a short term move.
"I knew that George was keen on Malcolm joining him at Derby and he's made him a good offer." Royle confirmed to the Official Club Website.
"We wish Malcolm well and have taken Andy Rhodes on board to work with the 'keepers here.
Webster Joins Derby
"It's a temporary move at the moment and no more than that. Andy was with me at Oldham and also played for Manchester City and Barnsley amongst other clubs."