Tatis, who signed a 14-year $340 million contract extension with the Padres last year, has missed all of the current season as he recovers from a broken left wrist.
Before the suspension, the native of the Dominican Republic had been expected to return to action in mid-to-late August.
Last season Tatis hit 42 homers, drove in 97 runs and finished third in National League most valuable player voting.
"We were surprised and extremely disappointed to learn today that Fernando Tatis Jr. tested positive for a performance-enhancing substance in violation of Major League Baseball’s Joint Prevention and Treatment Program and subsequently received an 80-game suspension without pay," said the Padres in a statement. "We fully support the Program and are hopeful that Fernando will learn from this experience."
The suspension means Tatis is not eligible for the post-season. The Padres currently sit second in the NL West behind the Los Angles Dodgers.
With only 48 games remaining in the regular season, Tatis' suspension will see him miss the early part of the 2023 campaign as well.
