A 34-year-old man was stabbed on a Manhattan subway early Monday for complaining about a fellow straphanger’s pitbull, police said.

The victim, who is homeless, was riding the northbound No. 2 train around 12:30 a.m. when he got into an argument with the other rider about the dog, authorities said.

The dog owner stabbed the victim in the left arm near his shoulder and fled when the train arrived at the 72nd Street stop, cops said.

The train car was covered in blood after the attack.

The victim was transported to St. Luke’s Hospital in stable condition.