The All-Star reliever was sent for an MRI after leaving Friday's game against the Arizona Diamondbacks due to discomfort in the back of his elbow.
Yates entered the game in the eighth inning and threw just six pitches, notching a strikeout while allowing the runner to reach base on a wild pitch on the third strike. He then departed the mound accompanied by a trainer.
"He said he felt good, and then he faced the first batter, and (the elbow) ... continued to irritate him," Padres manager Jayce Tingler said, according to Fox Sports San Diego.
Yates has morphed from a journeyman pitcher into one of baseball's best closers since arriving in San Diego in 2017. He saved an MLB-high 41 games last season while posting a 1.19 ERA, 0.89 WHIP, and 101 strikeouts with just 13 walks in 60 appearances. He was named an All-Star for the first time in his career, earned All-MLB first-team honors, and finished ninth in NL Cy Young voting.
But the 33-year-old has struggled in 2020. Though he's tallied two saves, Yates owns an inflated 12.46 ERA in six outings and has struck out eight batters while walking four.