Crawley Town have announced that manager John Gregory is stepping down from his position with immediate effect.
The 60-year-old, who took over at Broadfield Stadium last year, is to undergo major open-heart surgery in January which will require a lengthy period of recuperation.
Former Wolverhampton Wanderers boss Dean Saunders will take interim charge of the club.
Crawley are currently camped inside the League One relegation zone following an eight-game winless run.