The Herald understands the victim is a soldier with the NZ Defence Force.
A Defence Force was approached about the seriousness of any injury and a spokesperson confirmed a member "received medical attention in hospital after the incident at the Jet Park managed isolation facility in Hamilton".
"As the matter is before the courts we have nothing further to add."
Opetaia - who the Herald understands travelled from Australia - has pleaded not guilty to the charge and he is due to reappear in court in July.
Hamilton is home to three managed isolation and quarantine facilities - the Distinction Hamilton Hotel, the Ibis Hamilton and the Jet Park Hotel Hamilton.
Auckland has 18 MIQ facilities. There are six in Christchurch, two in Wellington and three in Rotorua.
Yesterday's official managed isolation and quarantine data showed that there are currently 2906 people carrying out their compulsory 14-day lockdown period in managed isolation facilities around the country.
A total of 83 people were currently in quarantine facilities around New Zealand.
The number of people projected to arrive over the next fortnight is 3815.
The total number of people who have gone through managed isolation and quarantine facilities in New Zealand since March 26 last year now stands at 136,000.