The Croatia star is adhering to a personal fitness plan devised by the Club as he self-isolates along with the rest of the nation.
But he can't wait to get back out there in 'proper' football sessions - and hopefully the conclusion of the Championship season.
"Every day is the same," he told bcfc.com. "It's boring. It's taking too long.
"It's the first time (as a footballer) that you're basically doing nothing. There's no training, no football.
"That is the situation. But I understand how important it is for us to stay at home until all this is over. This is a serious situation.
"I have an individual training plan to follow. I go for a run in the park. I do work in the little gym I have at home.
"But nothing can replace proper football sessions, training with your teammates in a competitive environment.
"Without proper training, without your teammates, without football . . . there is nothing that can replace it."
Based on the latest EFL advice full training cannot resume until 16 May. But even then that is not cast in stone.
Reflecting on his debut campaign for Blues after a big money transfer from Dinamo Zagreb, the combative midfielder says he is satisfied - to a degree.
"I think, look, I am new in this league, my first time abroad and I adapted quite quickly.
"In the Championship you play a lot of games. They come all the time. It is a fast, physical league. Every player is going to have times when they have a dip, play two or three bad games.
"I have played Champions League, Europa League. In my country. This is so different.
"I feel overall I have done OK, I am satisfied. I have been healthy, I have not had injuries.
"But I also know that I have areas I can improve in. I work hard, I always do. And I will continue to work hard to get better."
Sunjic says he really enjoys the English game and way of life.
"The culture of it over here, that's what I like. It's a new experience, an enjoyable experience. People live for the games, the atmosphere in the grounds is fantastic."
He confesses lining up again for Blues in action behind closed doors, as seems certain, will be odd.
"Of course it will be strange for all players, all teams. Not having fans will be unusual.
"If we get (to that stage) it will mean there has been progress. Life will start moving again.
"I think it is better to have football like that rather than no football."
Sunjic opted to stay in Birmingham rather than return home, where things are slowly changing.
"Because of the date we hope to train again if I had gone back to Croatia I would have to be quarantined for two weeks on my return.
"It makes sense to be here.
"In Croatia it is similar to England. Everything is shut down. But the government has given permission for all clubs to start training again.
"It will be in small groups, of five or six. That's good, it's a start. And they are going to gradually open up a bit in May, schools for the kids."