The crisis over the security forces' fierce response to a series of militant attacks is the biggest problem Suu Kyi has faced since becoming Myanmar's leader last year.
Critics have called for Suu Kyi to be stripped of her Nobel peace prize for failing to do more to halt the strife.
In her first address to the UN General Assembly as national leader in September last year, Suu Kyi defended her government's efforts to resolve the crisis over treatment of the Muslim minority.
This year, her party spokesman said she would not be attending, although he said he was unsure why.
"She's never afraid of facing criticism or confronting problems. Perhaps she's got more pressing matters here to deal with," Aung Shin, the spokesman, told Reuters.
International pressure has been growing on Myanmar to end the violence in the western state of Rakhine that began on August 25 when militants attacked about 30 police posts and an army camp.
The attacks triggered a sweeping military counter-offensive that refugees say is aimed at pushing Rohingya out of Myanmar.
Reports from refugees and rights groups paint a picture of widespread attacks on Rohingya villages in the north of Rakhine by the security forces and ethnic Rakhine Buddhists.
Soldiers and extremist Buddhists have reportedly been killing or raping the Muslims and setting their homes on fire.
The Myanmarese government says 400 people, mostly Muslims, have died in the latest bout of violence. The UN says the actual number likely tops 1,000.
Source: SBS News