Toronto police are looking for a man who sucker-punched a blind subway passenger earlier this week.

Mark Zillmann, 37, said he was transferring from the Bloor line train to the Yonge line on Tuesday when he was sucker-punched in the jaw.

"At first I thought something had dropped from the ceiling," the mild-mannered Mr. Zillmann told The Globe. "Then I realized that I'd taken a blow to the face from someone. It was a solid punch, but I didn't fall over."

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Before the attack, another disabled passenger had offered to assist Mr. Zillmann navigate the underground. The cane-carrying native of Zephyr, Ont., thanked the passenger (who was using a wheelchair), but assured the Good Samaritan that he knew his way around the subway station.

Moments later, he was struck flush in the face. Once he realized what had happened, he yelled for help. The cry was heard by the other passenger, who noticed a man fleeing. He attempted to pursue the assailant, but lost him at the escalator.

"He told me his name was Alfredo," Mr. Zillmann said of the unidentified Good Samaritan, whom he would like to thank. "He had a Spanish accent."

After the attack, TTC security staff responded to the scene and police were called in. Mr. Zillmann was transported by paramedics to Toronto Western Hospital with bruising to right side of the face. He was released the same night.

Toronto police are investigating the assault, which is just the latest random attack in the city. A 33-year-old is facing charges after a 68-year-old woman was head-butted at the Eaton Centre mall last Saturday.

TTC spokesman Brad Ross said any available surveillance video of Zillmann's assault would be turned over to police for their investigation. "All criminal matters of this nature are handled by Toronto Police Services," Mr. Ross said. "Our own special constables will be on the lookout for a suspect, and will make an arrest if the suspect is spotted."

As for Mr. Zillmann, a piano tuner by trade, he refuses to let the incident get the better of him. "I don't feel intimidated," he says. "I'm not going to let this stop me from getting around."