Singer Gavin DeGraw was hospitalized after he was viciously assaulted by multiple attackers late Sunday night in New York City ... TMZ has learned.
A source close to Gavin tells TMZ the singer -- who lives in New York City -- was outnumbered by several people during the attack.
Gavin's rep says he is still under observation at Bellevue Hospital tonight ... but would not be specific about his injuries.
Gavin has been touring with Train and Maroon 5 ... and their next stop was scheduled for Tuesday night in Saratoga Springs, NY.
Story developing ...