Tanaka's seven-year, $155 million contract allows him to terminate the deal after this season, give up a $23 million annual salary from 2018-20 and become a free agent.
"It's something that I put aside going into the season," Tanaka said Wednesday through a translator. "Can't be really thinking about that while you go through the season, really focus on this season and when the time comes after the season, then I'll probably have a chance to think about that more."
Tanaka arrived at the Yankees' minor league complex Monday for pre-spring training workouts. The 28-year-old right-hander threw off a bullpen mound Wednesday.
"Felt better than I thought I would be," Tanaka said. "I went out there and I think I was able to throw with some force. Felt good about where I'm at now. I feel that I'm a little bit ahead of schedule compared to last year."
Tanaka was a concern at the start of spring training last year after arthroscopic surgery in October 2015 to remove a bone spur from his throwing elbow. He went 14-4 with a 3.07 ERA in 31 starts.
Tanaka had planned to pitch for Japan in the World Baseball Classic next month but decided not to participate.
"I had to take into consideration a lot of things," he said. "It was more of I was able to go through a whole season finally last year, and I understand what the team is looking for from me."
Tanaka is 39-16 with a 3.12 ERA over 75 starts in three seasons with the Yankees. He was limited to 44 starts over his first two seasons due to injuries.