NEW YORK -- The head of the baseball players' association thinks a shorter pitch clock has contributed to a series of pitcher injuries.

"Despite unanimous player opposition and significant concerns regarding health and safety, the commissioner's office reduced the length of the pitch clock last December, just one season removed from imposing the most significant rule change in decades," union executive director Tony Clark said Saturday night in a statement.

"Since then, our concerns about the health impacts of reduced recovery time have only intensified," Clark said. "The league's unwillingness thus far to acknowledge or study the effects of these profound changes is an unprecedented threat to our game and its most valuable asset -- the players."

Cleveland's Shane Bieber, Atlanta's Spencer Strider, the New York Yankees' Jonathan Loáisiga, Miami's Eury Pérez and Oakland's Trevor Gott are among the pitchers diagnosed with elbow injuries.

Major League Baseball pushed back on the union's statement, pointing to a three-decade increase in pitcher injuries despite the clock being implemented just last season. MLB said that UCL surgeries at the minor league level actually declined in 2022, the first year that the pitch timer was used across the minors. The league believes the increase in max-effort pitching and focus on pitch design have contributed to the rise in injuries more than the clock.

"This statement ignores the empirical evidence and much more significant long-term trend, over multiple decades, of velocity and spin increases that are highly correlated with arm injuries," MLB said in a responding statement Saturday.

MLB said it is undergoing a research study into causes of increased injuries. It cited an analysis by Johns Hopkins that "found no evidence to support that the introduction of the pitch clock has increased injuries" and "no evidence that pitchers who worked quickly ... or sped up their pace were more likely to sustain an injury than those who did not."

Additionally, the league pointed to more players entering professional baseball with significant injury history, which can be a precursor to repeat issues. It said that, on average, only six players between 2011-13 already had UCL reconstruction before they were drafted and that the number reached 24 players from 2021-23.

Cleveland said Saturday that Bieber, the 2020 AL Cy Young Award winner, will have season-ending Tommy John elbow surgery to repair an injured right ulnar collateral ligament.

A few hours later, Atlanta said Strider had a damaged UCL and will be examined further by Texas Rangers team physician Dr. Keith Meister.

Loáisiga said Saturday he needs season-ending elbow surgery and will be sidelined for 10 to 12 months. A 29-year-old right-hander, Loáisiga said he felt a pop in his elbow while throwing a changeup to Jorge Barrosa, his final batter in the ninth inning of Wednesday's 6-5, 11-inning win at Arizona. A scan revealed a torn UCL.

Miami said Thursday that Pérez will have Tommy John surgery and miss the season. A day earlier, Gott had TJ surgery.

MLB instituted a pitch clock for the 2023 season set at 15 seconds with nobody on and 20 seconds when there was a baserunner. The average time of a nine-inning game dropped to 2 hours, 40 minutes, a 24-minute decrease to its shortest since 1985. The 11-man competition committee decided in December to cut the clock to 18 seconds with baserunners, a change that was opposed by the four players on the body.

ESPN's Jesse Rogers and The Associated Press contributed to this report.