Nelson has been charged with one count of first-degree assault and one count of third-degree assault for allegedly kicking 24-year-old Isaac Kolstad in the head during an altercation this weekend in downtown Mankato, Minnesota, leaving Kolstad gravely injured.
"The Rutgers football family's thoughts and prayers are with Isaac Kolstad and his family," Scarlet Knights coach Kyle Flood said in a statement.
Nelson, 20, kicked Kolstad in the head while Kolstad was lying on the ground after being struck by another man early Sunday morning, according to a criminal complaint. Kolstad, 24, a former linebacker at Minnesota State, Mankato, remained in critical condition Wednesday with a severe head injury.
The complaint also said witnesses described Nelson as being upset over attention being paid to his girlfriend.
A police sergeant who reviewed surveillance video described Kolstad striking Nelson in the back, then moving away and being pursued and struck by an unidentified man. Authorities announced Tuesday that a second suspect -- Trevor Stenner Shelley -- has been arrested after witnesses identified Shelley, 21, as the man suspected of punching Kolstad and knocking him to the ground.
Shelley was charged with two felony assault counts and had his bail set at $20,000 on Wednesday. He's due back in court May 22.
"Nelson pushes past others, approaches I.K. and delivers at least one kick to the left side of I.K.'s head," the complaint reads. "Sergeant Knutson noted that the video clearly shows that I.K. was defenseless as Nelson delivers the kick or kicks to the head."
"Isaac had surgery early this morning. It went well. Isaac remains in critical condition," Kolstad's family said on its CaringBridge website Tuesday.
Nelson appeared in court Monday wearing an orange jail jumpsuit, his hands cuffed and his ankles chained. Afterward, his attorney, Jim Fleming, said it wasn't certain who caused Kolstad's injuries, suggesting the man being sought by police "threw a debilitating blow to the victim."
Fleming said Nelson "was not an aggressor in this situation."
Nelson was a top recruit when he came out of Mankato West as the state's Mr. Football in 2011, and he spent much of his first two seasons at Minnesota as the Golden Gophers' starter. He played in 11 games last season but announced afterward that he would transfer to Rutgers and what he said was a more pass-friendly offense. He threw for 1,306 yards, nine touchdowns and six interceptions last season and ran for 364 yards.
He would have had two seasons of eligibility left after sitting out next season.
ESPN's Joe Schad and The Associated Press contributed to this report.