MANKATO, Minn. >> A former Minnesota State linebacker was in critical condition Monday after an alleged assault that police said involved the former quarterback at Minnesota.

Isaac Dallas Kolstad, 24, of Mankato, was in critical condition at the Mayo Clinic Health System in Mankato, according to hospital spokesman Kevin Burns. Police said they found Kolstad while patrolling the city’s downtown entertainment district early Sunday and arrested former Minnesota quarterback Philip Nelson at the scene.

“He is young and strong, but the battle he has in front of him is enormous,” Kolstad’s family said on its CaringBridge website. “We do know that his brain did sustain permanent damage. We do not yet know to what extent and won’t for many days. He is very sick.”

Nelson, 20, was taken to the Blue Earth County jail, according to a police statement. He remained in custody Monday pending possible charges of third-degree assault. A message left with Nelson’s parents Monday was not immediately returned.

Police said they are searching for another person who may have been involved.

Steph Stassen, a graduate student who said she witnessed the assault, told the Star Tribune that the bars had just closed when “all of a sudden, this guy comes out of nowhere and sucker punches” Kolstad. Stassen and her roommate said another person, not Nelson, threw the punch, but that a man she later learned was Nelson then kicked Kolstad in the head “like it was a soccer ball — just out of nowhere.”

Nelson left the Gophers in January to transfer to Rutgers, which is moving into the Big Ten conference next season. He played in 11 games last season, but said Rutgers offered a more pass-friendly offense. He completed 50.5 percent of his passes for 1,306 yards with nine touchdowns and six interceptions last season. He also rushed for 364 yards and six touchdowns while sharing quarterback duties.

“We are in the process of gathering information on the situation and reserve comment until the legal process is complete,” Rutgers athletics spokesman Jason Baum said in a statement.

A candlelight vigil for Kolstad was held at Minnesota State University in Mankato on Sunday night, according to The Free Press of Mankato.

Sam Thompson, who said he played football with Kolstad for three years, told The Associated Press he was with Kolstad on the night of the assault but didn’t want to comment out of respect for his family and the investigation.

But he said Kolstad has a 3-year-old daughter and that his wife is pregnant.

“A recurring theme in his life is the importance of family,” Thompson said. “He’s got such a beautiful family that he’s just starting … He’s just a family guy. He loves his daughter so much and is looking forward to the birth of his second child.”

Thompson said Kolstad graduated in December and recently started working at Fastenal, a local company.

Thompson said Kolstad was a leader on and off the football field.

“His personality is one people wish they had,” Thompson said. “He is just one person … that people gravitate toward.”