Police said it happened last Tuesday around 11:30 p.m. at the Washington Blue Line stop on North Dearborn Street in the Loop.
Investigations say the suspects approached the victim, a 49-year-old man, and began punching him repeatedly.
The suspects are described as being 15-23 years old and 5-foot-8 to 5-foot-11. They weigh about 160-180 pounds.
The suspects wore white T-shirts with black jeans, and one of them was also wearing a grey Nike hooded sweatshirt.
Police asked anyone with information to call them.
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