The Atlanta Braves are scrambling to regroup after learning Sunday night that star outfielder Ronald Acuna Jr. will miss the rest of the season due to a torn ACL in his left knee that he suffered during a win over the Pittsburgh Pirates earlier in the day.

Atlanta begins battling through its latest dose of adversity on Monday when it opens a four-game series with the visiting Washington Nationals.

Acuna, the reigning National League MVP, doubled to lead off Sunday's game. With one out, he was attempting to steal third when his left knee buckled, and he fell to the ground in pain. Acuna walked off the field gingerly with what the team initially called "left knee soreness." An MRI exam later revealed the extent of the injury.

"I saw the catcher throwing the ball back to the pitcher very slow," Acuna said through an interpreter after the game against Pittsburgh. "I was timing that so I could steal third. But in that moment, he threw it hard. So I had to come back, and that's when I felt it."

Acuna missed much of the 2021 season after tearing the ACL in his right knee. He also sprained his left ACL in May 2018 and was sidelined for just over a month.

The Braves hope help will be on the way soon, as they might get a pair of All-Stars back in the lineup when they begin the series with Washington on Monday.

Atlanta is expecting catcher Sean Murphy and third baseman Austin Riley to return, possibly for the series opener. Murphy has missed 49 games with a strained left oblique. Riley has missed 13 games with left side tightness.

The pitching matchup for Monday's game features Atlanta right-hander Charlie Morton (3-1, 3.35 ERA) and Washington lefty Mitchell Parker (3-2, 3.32).

This is the first meeting between the teams this season. Atlanta salvaged a win in the three-game series against Pittsburgh with an 8-1 victory on Sunday, while Washington had a two-game winning streak broken with Sunday's 9-5 loss to the Seattle Mariners.

Morton's experience showed in his most recent start, which came against the Chicago Cubs last Tuesday. Morton worked five innings and allowed two runs (one earned) on four hits to go along with four walks and eight strikeouts. It was the fifth time in six starts that Morton has limited the opposition to two runs or fewer.

Morton has made 16 career starts against the Nationals, going 6-6 with a 4.69 ERA. His last appearance against Washington came on Sept. 22, 2023, and he left the game after one inning due to right index finger discomfort.

Parker, who has never faced the Braves, will be making his eighth career major league start. He has allowed three runs or fewer in each of his first seven starts.

In Parker's latest start -- against the Minnesota Twins last Monday -- he went six innings and allowed three runs on seven hits, walking one and striking out seven to earn his first victory since April 21. Parker allowed a home run in the sixth inning but was able to finish the frame without further damage.

"We thought about taking him out, but I wanted to see what he could do," Washington manager Dave Martinez said of Parker. "We had a big enough lead. I wanted to see him get through it and he did."