The number 24 world has a gym set up at home, and a private tennis court is used.
"These days I spend more time working out than in training. I can't really do anything else, "Fritz told Reuters Monday.
Fritz said if the tour restarted and believes his extra work during isolation could pay dividends when play resumes, he could play tomorrow.
"I could (play) this very moment. I practiced enough to keep my level and then I am in the best shape ever with all the gym stuff I've been doing, "he said.
"I'm willing to go"
"I think this time will be really interesting when all the players come back to play, because then you'll see which players took the time to work on their fitness and get stronger and what players weren't working during that time."
The coronavirus outbreak has been playing havoc with tennis season, causing Wimbledon to be cancelled and pushing back the French Open until September.
Organizers of the tournaments are hopeful the U.S. Open, scheduled to start on August 25 in New York, could go ahead but Fritz is not so sure.
"They're aiming for some time, but I think the time is unrealistic a little bit," he said.
"The purpose is to play for the U.S. Open, but I don't know how they will be able to do that personally.
"They want to be optimistic but as it continues to be pushed back it is tough."