City are due to face Wellington Phoenix in a rescheduled FFA Cup quarterfinal on Wednesday night, 17 days since they were last in action.
Kisnorbo said he couldn't guarantee City would be ready to play, and he'd make an assessment of which players were fit after Tuesday's training.
- ESPN+ viewers' guide: LaLiga, Bundesliga, MLS, FA Cup, more
"We've only had maybe five that haven't had COVID ... it's been crazy," he said. "We have players that are available for selection ... what the bench will be, I don't know, what the starting 11 will be, I don't know.
"We have boys returning but how they feel, I don't know. Some of the boys have only been training for two days.
"We're going to be unknown. We have to adapt."
Kisnorbo said current cases were limited to "two young boys," and that coaching staff "had been OK."
"The main thing is the health of the players is most important," he said.
Wellington travelled to Melbourne last month for the fixture only to turn around and fly home when Football Australia postponed the game hours prior to kick-off.
Despite Kisnorbo's concerns, Phoenix coach Ufuk Talay said they had an undertaking from FA head office the match would go ahead.
"We got information from the FFA the game is good to go," he said. "We need to play these games or there's going to be a massive backlog."
The Nix will miss two of their own as they recover from coronavirus, with Talay saying the club may have avoided greater spread given players weren't able to spend time with family over Christmas.
"The players are trying to be smart in the decisions they make," he said. "Hopefully not clubbing. Our players are pretty young ... half of them wouldn't get into nightclubs anyway."
Wellington are in the last eight for the first time and eye an FFA Cup run as a tonic to four straight league defeats.
ALM leaders Victory are also in cup action on Wednesday night, against Adelaide.
Central Coast have already qualified for the last four, beating three lower-league opponents.