Durrant has the Scottish club where he had been working as a coach since 2005. The former Scotland international midfielder spent 14 years as a player at Rangers.
During his time in the Gers’ coaching set-up, the 49-year-old held several positions. Durrant spent last season in charge of the Rangers Under-20 development squad.
Robertson has explained why the Scottish Premiership-bound club have decided to part company with Durrant.
“Ian has been such a big part of this club for so many years,” the Rangers managing director told the club’s official website. “He has a special place in Rangers’ history but clubs are forever changing and evolving and sometimes that means a change in personnel."
Durrant had a very successful playing career with Rangers, winning every major domestic honour possible.
The former Scotland international midfielder joined Rangers' first-team coaching staff when Walter Smith came back for a successful second spell in the dugout.
Rangers won the Scottish Championship title this past season and will feature in the Scottish Premiership during the 2016-17 campaign.
Mark Warburton’s side also clinched the Scottish Challenge Cup and reached the final of the Scottish Cup.
The Gers will be aiming to compete with Old Firm rivals Celtic for the Scottish Premiership title next season.