Police have arrested a rising basketball star from Winnipeg's inner city after a serious assault in the West End that sent a 20-year-old woman to hospital in critical condition.

"This is a horrific assault," ​Winnipeg police Const. Rob Carver told reporters Wednesday. "The injuries were unbelievable."

Police responded to the area of Dominion Street near Ellice Avenue at about 2:30 a.m. CT Tuesday after reports of an assault.

Before officers arrived, a Good Samaritan driving through the area noticed what had happened and stopped to help, and a man armed with a knife stole the driver's vehicle and sped off, police said.

Police blocked part of Ellice Avenue between Downing Street and Garfield Street North Tuesday morning after what they described as a serious assault. (Sabrina Carnevale/CBC)

Officers arrived to find a woman with serious injuries. She was rushed to hospital in critical condition but is now stable.

RCMP arrested 21-year-old Junior Sesay from Winnipeg on Highway 10 near the U.S. border. He was charged with attempted murder, robbery, and breaking and entering.​

Investigators believe the attack wasn't random as Sesay and the woman are known to each other. The woman, who is a University of Winnipeg student, was in a relationship with Sesay's brother, Carver said.

Carver said the most serious part of the assault happened on the street after the woman ran outside out of a home.

"For our investigators and for the people involved in this ... it's been difficult, nowhere near as difficult as it's been for the people directly involved, people who know her, her family."

Carver said Sesay was known to police before the attack, but police did not elaborate. Sesay has no criminal record in Manitoba.

Sesay was known in the West End as a rising basketball star. In 2013, CBC News reported that Sesay was a standout player with the Oak Park Raiders when he was in high school, and spent about three hours playing basketball every day.

He spoke to CBC about wanting to give back to the community.

Junior Sesay spoke to CBC News in 2013 about his love of basketball. (CBC)

The Sesay family — three boys and a single mom — came to Canada from war-torn Sierra Leone when the children were young, according to a 2015 CBC News report about the basketball accomplishments of Sesay and his brother.

Settling in Winnipeg wasn't always easy and the family struggled to get by, Sesay's brother said, adding basketball scholarships helped the brothers attend university.

That report said Sesay was playing for the University of Victoria's men's basketball team. He only played one season before returning to Winnipeg.