Monfils reached a career high ranking of seven last year but has since dropped to 78th after a succession of injuries.
His most recent problem, a persistent discomfort in his right knee, ended his 2012 season last month after he had reached the quarter-finals in Metz in September.
Before Chamagne, the 26-year-old was trained by Roger Rasheed who now works with Jo-Wilfried Tsonga.
"I want to thank Patrick for his investment and his presence at my side during this period. I wish him much success in his future endeavors," Monfils said.
Monfils is expected to be back in action in time for the beginning of the 2013 campaign, starting with the early January tournament in Doha ahead of the Australian Open.