The 31-year-old Frenchman has dropped down the world rankings in 2017 having reached a career high of sixth last November and he is now sat in 36th position.
An ongoing knee issue, which forced him to retire from his US Open third-round tie against David Goffin, has hampered his progress this year and prevented him from picking up any titles.
Monfils has also been forced out of this weekend's Davis Cup tie as France are facing Serbia, but could return for some of the season-ending indoor events.
Meanwhile his agent Nicolas Lamperin has revealed that Monfils is using his time off the court to plot further ahead to the New Year.
"Unfortunately, Gael was forced to withdraw from the Davis Cup semi-final a few days before the tie against Serbia following his knee injury contracted over the summer which prevented him from performing at his best at the US Open. He remains nevertheless their biggest fan and wishes them all the best for the tie," Lamperin said, per Monfils' Facebook page.
"He now needs to rest and get treatment for some time before he can get back to practice and then tournaments when ready. We have used this time off to start working on his schedule for next season."