CINCINNATI -- In what could be a blow to the Reds' efforts to remain in the postseason chase, the best season of Reds All-Star starting pitcher Hunter Greene's young career has been interrupted by an injury.

Before Cincinnati's 13-1 loss to the Royals at Great American Ball Park on Saturday night, Greene was placed on the 15-day injured list with right elbow soreness. Cincinnati announced that a corresponding move would be revealed on Sunday.

“We put him on the IL for precautionary reasons," Reds president of baseball operations Nick Krall said. "We are going to get him an MRI in the next couple of days, and we’re just going to try and figure that out.”

Greene, 25, is 9-4 with a 2.83 ERA in 24 starts this season. The first-time All-Star in 2024 has struck out 162 batters in 143 1/3 innings, and leads the National League by allowing just 5.8 hits per nine innings. He does lead the NL in batters hit by a pitch (19) and is second in walks allowed (53).

On Tuesday during a 4-1 win over the Cardinals, Greene allowed one earned run over seven innings.

“He had some stuff after the start. He felt fine and then today [while] playing catch, he felt it again," Krall explained. “We’ll have more information in the next couple of days.”

The Reds will likely call up a reliever on Sunday, but will need a starter to take Greene's rotation turn on Monday at Toronto. Because of injuries to Graham Ashcraft and Brandon Williamson, their starting pitching depth is thinner.

Right-hander Julian Aguiar, who is ranked No. 11 in the organization by MLB Pipeline, could be a leading candidate for his first big league call-up. Aguiar has a 3.79 ERA over 22 starts with Double-A Chattanooga and Triple-A Louisville, where he was promoted on June 22. Another possibility with Louisville is Connor Overton. Casey Kelly, who until recently was pitching in Korea before signing a Minor League deal with the Reds, is also with Louisville, but he got the start for them on Saturday, so he won't be available to start on Monday.

The organization's No. 2 prospect (No. 35 overall), Chattanooga's Rhett Lowder, is not expected to receive a promotion.

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During each of his first three big league seasons, Greene has missed time on the IL. He missed 71 days in 2023 with right hip pain and six weeks in 2022 with a right shoulder strain.

In 2018 while in the Minor Leagues, Greene tore the ulnar collateral ligament in his right elbow. After treatment and rehabilitation failed, he underwent Tommy John surgery on April 9, 2019.

When asked if there was added concern because of Greene's elbow history, Krall declined to comment.

“As of right now, I don’t want to speculate," he said. "We’ll have the doctor check him out, and go from there.”

Over his last seven starts, Greene moved briskly into NL Cy Young Award contender status by going 4-0 with a 0.98 ERA while working at least six innings in each of them and seven innings four times. He is a key reason the Reds entered Saturday four games back from the final NL Wild Card spot despite a record under .500.

The IL move for Greene was retroactive to Aug. 14, which would enable him to miss a little less time if there is no serious issue.

“Hopefully this is a minor setback, and he continues to grow," Krall said. "He’s been tremendous this year. When I talked to him, it’s a tough thing to have that conversation with him. He understood as well. He knows he will miss at least one start. This was the best way we could do this from a precautionary standpoint. Hopefully, this is going to be the best-case scenario and move forward.”