Rays third baseman Yandy Diaz hit a hot shot off Tanaka's foot, but it ricocheted directly to first baseman Luke Voit, who touched first for the out:
Tanaka was through 88 pitches at the time and had allowed three hits, no walks and no runs, which suggests that he would have continued pitching if not for the potential injury.
After recording the final out of the inning, Tanaka appeared to yell in frustration.
Tanaka has been able to avoid major injuries throughout his major league career, although various issues have continually kept him off the field.
He missed about a month last year because of hamstring problems after shoulder problems limited him in 2017. Several trips to the injured list have prevented him from reaching 200 innings in any of his first five years with the Yankees.
While he was only one out short of reaching this milestone in 2016, the 30-year-old still only averaged 26 starts from 2014 to 2018.
Tanaka remains an effective pitcher when he is healthy, although he can be inconsistent at times.
Entering Saturday's game, Tanaka was 3-3 with a 3.44 ERA, 1.20 WHIP and 47 strikeouts in 52.1 innings over nine starts.
He also had a 12-6 record and 3.75 ERA in 2018, marking his fifth straight season with at least 12 wins.
The Yanks can ill afford to lose Tanaka for any period of time since their starting rotation has already been struck heavily by injuries this season. Both Luis Severino and James Paxton are currently on the injured list.
If Tanaka lands on the IL as well, it will put even more pressure on Domingo German, J.A. Happ and CC Sabathia to lead the way.