A man was stabbed in the back on a Brooklyn train early Wednesday by a trio of robbers who made off with just $30, cops said. 

The victim was riding a southbound No. 5 train approaching the President Street station in Crown Heights around 6:30 a.m. when three suspects approached him and tried to rob him, sparking a struggle, authorities said. 

The trio picked up his wallet and pulled $30 out of it, cops said. 

When the doors opened at the station, the suspects stabbed him in the back and ran off the train, police said. 

The victim suffered a small puncture wound, cops said. 

The victim stayed on the train until the Church Street station, and was taken to the Kings County Hospital Center with non-life-threatening injuries. 

The assailants were still in the wind later in the morning.