The incident was reported just after 5 p.m. on a northbound N train.
Authorities said their initial investigation revealed the suspect demanded the 42-year-old victim's phone.
When he did not comply quick enough, he was shot in the left leg.
"The male suspect with the gun fired one time, striking the victim in the left leg," NYPD Transit Assistant Chief Vincent Coogan said.
As the train entered the Union Square station, the suspect fled onto the platform, followed by a male who witnessed the attempted robbery.
Police are looking for one suspect in connection to the incident.
Thankfully, officers were at Union Square and applied a tourniquet to the victim's leg to help stop the bleeding.
The victim was taken to a Bellevue Hospital treatment.
"Last thing we need is for anyone to die, especially when we're on the scene -- so make sure to get that tourniquet on as fast as possible," NYPD officer Rajandeep Singh said.
"I'm just happy that I actually came into work today and actually made a difference," NYPD officer Elijah Pardiu said.
Detectives are scouring surveillance cameras hoping to find the shooter before he pulls the trigger again.
"The subways are safe, statistically speaking, but they also have to feel safe," said Janno Lieber, Acting MTA Chair and CEO.
And that's the point. Riders tell Eyewitness News they don't feel safe at all.
"I've been traveling on the subway for last 27 years. Never has this been this bad," one subway rider said.
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