A 15-year-old detainee at the Don Dale youth detention centre was denied medical treatment for a broken collarbone for at least two days and guards would not allow him to wear a sling, a royal commission has heard.

In a written statement to the Royal Commission into the Protection and Detention of Children in the Northern Territory, the former detainee, known only as BF, said that in spite of the injury in early 2011 he was told to play sports and later broke his collarbone again.

BF is one of the witnesses giving evidence to the royal commission whose identity has been suppressed.

He gave oral evidence in a closed session at the royal commission hearings in Alice Springs on Monday but his written statement was released with redactions.

In the statement, he said he suffered the injury when he was tackled by an older detainee during a rugby game at Don Dale.

Claims BF forced to mop floors with broken collarbone

He said he complained to guards about pain that prevented him from sleeping but was still forced to do chores such as vacuuming and mopping floors.

"All of these activities were very painful," the statement read.

He said a female guard on duty on the day of the injury told him she would put in a medical form so he could be seen by a doctor but two or three days later another guard he got on well with, Michael, said he could not find a form about the injury.

Once he received medical treatment, BF said a doctor told him to wear a sling for six weeks.

'Sling denied because of hanging risk'

The statement said that even though a guard was told of the doctor's instructions, some guards thought the sling was a strangling risk and did not let him wear it.

But BF said at that time, he was not threatening self-harm.

"Some of the guards, mostly the older guards, would let me wear the sling, but most of the new guards didn't," the statement said.

He said a month after his injury, information about his collarbone had been rubbed off a white board where detainees' medical conditions were recorded.

'I still can't lay down on that side of my body'

BF said a few months after the incident when he broke his collarbone again, he was angry because he believed it was a result of being told to play sports.

"I still feel my collarbone click when I move it around. I still can't lay down on that side of my body because of the pain," BF said.

Around the same time, BF said his mother died and he was forced to spend several days in a "little white room" for people at risk of self-harm even though he had not told anyone he was at risk.

"I kept explaining that what I needed was sunshine and support from my family and friends, as some of my cousins were in Don Dale at the time, but I was ignored," the statement said.

He said during his time in the room he was seen by a doctor but not a counsellor.

According to BF's statement, he was about 12 years old when he first attended court for stealing bikes and his offending escalated after his parents' separation and again after he entered Don Dale for the first time.

In the statement, BF said he was no longer in detention and his experience in Don Dale turned him off going back there again.