Club chairman Dursun Ozbek released a statement confirming the news and vowing to install a new head coach imminently.
"After our board meeting, we decided to part ways with Riekerink and we've informed him about this decision," Ozbek told reporters. "We want to assign our new coach as soon as possible."
Riekerink lifted the Turkish cup with Galatasaray last May but his charges have struggled to keep up with the pace set by bitter rivals Besiktas in this season's Super Lig.
Former Juventus and Chelsea defender Igor Tudor has been named as a favourite to replace Riekerink, reports Goal.com.