Montreal police will investigate after a 22-year-old man said his eye was badly injured by the blast of a police stun grenade during Wednesday’s student protest over tuition fee hikes.

Francis Grenier, a student at Cégep de Saint-Jérôme, told CBC News from his hospital bed that he doesn't know if he'll regain vision in his right eye.

This photo of Francis Grenier was posted on social media after he was injured during student protests Wednesday. (Facebook)

Student movement leaders are calling him a victim of police brutality and are accusing riot squad officers of overreacting after snowballs were launched during the afternoon protest on Sherbrooke Street.

Grenier said he was in front of the Loto-Québec headquarters Wednesday afternoon playing the harmonica when an officer told him to leave.

He said he was starting to leave the area when riot squad officers started launching stun grenades over the crowd. One grenade missed him, but a second detonated close to his face, he said.

He underwent surgery overnight for a detached retina.

"I didn't do anything wrong," Grenier said. "The police, they didn't [give] us enough time to leave. That's what happened."

Four people were reportedly injured during the latest in a series of escalating protests over tuition fee hikes in Quebec.

Police initially said all of those injuries were minor, although two of the people — one police officer and one protester — were whisked to hospital by ambulance to be treated for trauma.

A photo of Grenier with a bloodied right eye was posted on Facebook.

Montreal police said it's too early to conclude how he was hurt.

Insp. Philippe Pichet said officers have spoken with Grenier in hospital and are reviewing videos to verify his account.

"We’re not sure at this time what exactly caused the injury, but we are aware of that situation," he said.

Pichet said police were trying to disperse the crowd outside the building before removing the people inside trying to occupy it when the stun grenades were fired.

The crowd was given warning by the tactical officers before they were pushed back.

"We tried different ways to disperse the crowd," he said. "We took some stun grenades that we have to put very high in the air because we want them to explode, to make the noise, about eight feet above the people who were in the street at that time."

He said they are reviewing the incident and will make adjustments to their operations if necessary.

"If we have to use different methods, different equipment, we’ll do our best," he said. "Our goal is not to injure the people who are doing some demonstrations, it’s to ensure the safety of everybody around that."

More student demonstrations are planned for Thursday in Montreal.