Former Minnesota State University, Mankato, linebacker Isaac Kolstad sustained permanent brain damage from injuries following an alleged assault in which Rutgers quarterback Philip Nelson was arrested Sunday morning.

Blaine Kolstad, Isaac's father, wrote on Sunday night that his 24-year-old son is in critical condition. Kolstad had surgery to place a pressure gauge in his skull and may need additional operations.

"He is currently in critical condition and fighting for his life," Blaine Kolstad wrote. "He is young and strong, but the battle he has in front of him is enormous. ... 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. Please pray for Isaac and all of those involved."

Nelson, who transferred from Minnesota to Rutgers earlier this year, was arrested at the scene and put in jail Sunday on suspicion of assault after officers found Kolstad in the Mankato downtown entertainment district at 2 a.m.

Kolstad was taken to Mayo Clinic Health System in Mankato.

After playing two seasons at North Dakota State (2008-09), Kolstad sat out 2010 and spent his junior and senior years at Minnesota State. He started 12 games his senior season and finished third on the team with 59 tackles.

Minnesota State held a candlelight vigil for Kolstad on Sunday evening.

Radio station KTOE-AM reported that police recommend felony charges of third-degree assault against Nelson.

After spending two years at Minnesota, Nelson announced in January he was transferring to Rutgers. The 20-year-old took part in spring practice at Rutgers and is sitting out this season because of NCAA transfer rules.

Nelson started nine of the 11 games he played last season but chose to transfer because of Rutgers' more pass-friendly offense. He completed 50.5 percent of his passes for 1,306 yards with nine touchdowns and six interceptions in 2013. He also rushed for 364 yards with six touchdowns.

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

Nelson is expected to be arraigned Monday or Tuesday.

Police are seeking a second suspect.

"It's an ongoing investigation, and as more information becomes available, we'll be releasing it," city spokeswoman Shelly Schulz said Sunday.