"@Gael_Monfils withdraws from #RG16 because of a bad virus. Get well soon and see you for #RG17 Gael," they said in the official French Open Twitter feed.
The 29-year-old Frenchman joins world number three Roger Federer, who pulled out of the year's second grand slam on Thursday citing a lack of fitness.
Monfils, who reached the quarter-finals of the Australian Open this year, has had a mixed tour so far, having not getting past the second round in the Madrid and Italian Open this month, but reached the final of the Monaco Open in April.
Monfils has never gone past the semi-finals of the French Open and was knocked out in the fourth round by Federer last year.