The move came after a video emerged of the fight that led to his arrest early Tuesday morning and subsequent charges for assault and battery and being drunk in public.
TMZ Sports released the video Wednesday showing Nicholson punching another man on a street five minutes from Redskins Park. Nicholson and a female companion were arrested for attacking another couple, according to a Loudoun County police report.
Nicholson's 24-year-old companion, Sydney Maggiore, was charged with malicious wounding and assault and battery.
The league rules for the reserve/non-football illness list are the same as with the physically unable to perform list, meaning Nicholson will have to sit out six weeks, rendering his season over. He does not occupy a roster spot during this time.
Earlier Wednesday, Redskins coach Jay Gruden had said that Nicholson wouldn't play Saturday against the Tennessee Titans. The Redskins (7-7) have two games remaining and remain alive in the playoff race.
Gruden said they were aware of the video and planned to look at it after meeting with the media. The video emerged while the Redskins were at practice. Gruden said they also were planning to speak with Nicholson before making a decision. Hours later, Nicholson was put on the non-football injury reserve list.
The 39-second video showed part of the incident that led to the arrest around 2 a.m. outside World of Beer in Ashburn. It showed the other man on top of another female with Nicholson either trying to pull him off or fighting him. It's uncertain if the female was Maggiore. Another man was trying to contain Nicholson, but Nicholson pulled away.
As the man stood up, Nicholson hit him with two left-handed punches, the second of which knocked the man to the ground. The man got back up and, as another man tried to hold off Nicholson he again pulled away and knocked the man to the ground.
The police report states that "an investigation determined the male suspect assaulted the male victim, and the female suspect struck the female victim with a bottle and also assaulted the male victim."
The report also says one of the victims claimed the altercation occurred after the "suspects pulled up in a vehicle and honked the horn at them." Nicholson and Maggiore returned to the scene after deputies arrived. The two alleged victims were treated at a local hospital for injuries that were considered serious but not life-threatening.
Redskins corner Josh Norman said he didn't want to discuss the situation because he didn't know all the details. He said he did reach out to Nicholson.
"That goes without saying," Norman said. "He's still going to be at our [group] dinner tomorrow. It's what it is. But I don't know the full details of what happened. We'll figure it all out. I guess on the organization side if they want to do something, that's on them. I don't know."
Redskins linebacker Mason Foster said, "I haven't talked to him. He's going through a lot. I don't really know the details. I'll support him fully and wholeheartedly, man. That's my brother."
Nicholson, a second-year safety, started the first seven games but lost his job when the Redskins traded for Ha Ha Clinton-Dix. Nicholson has not played in the last four games.
The Associated Press contributed to this report.