PHILADELPHIA -- Marlins manager Don Mattingly had an optimistic outlook entering the second half of the 2021 season.

Sure, the Marlins came out of the All-Star break in last place in the National League East, but they were only nine games back of the first-place Mets in a division that featured only one team with a winning record. They were also kicking things off with a seven-game divisional road trip against the Phillies and Nationals -- a prime opportunity to close the gap in the standings.

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Instead, Miami is departing Philadelphia having lost three of four games -- and potentially three of its best players. Jazz Chisholm Jr. departed in the first inning of Sunday's 7-4 loss against the Phillies at Citizens Bank Park due to a left shoulder contusion. Garrett Cooper then exited in the bottom of the eighth with a left elbow injury after his arm bent awkwardly as he attempted to catch a throw from catcher Jorge Alfaro on a bunt attempt. That all came after Miami started the day by dropping a 4-2 decision in the completion of Saturday's suspended game.

X-rays on Chisholm were negative, while Cooper was still being evaluated at the time Mattingly spoke to the media after the game. Both players are expected to undergo further testing on Monday in D.C., when the team opens a three-game set against the Nationals.

"Kind of one of those days; you start off hopeful where you're at, and hopefully able to put two on the board, and you don't get either one,” said Mattingly, whose club dropped to a season-worst 13 games below .500. “Then you see Jazz go down and you see Coop go down.”

Chisholm sustained the injury as he attempted to make a sprawling catch on Bryce Harper's bloop single with two outs in the bottom of the first. He came up short on the play, landing awkwardly on his left shoulder in shallow right field. Mattingly and the training staff immediately ran out to check on Chisholm, who was in obvious pain as he walked off the field with his left arm pinned to his side while his right arm covered his face.

Though he has cooled off a bit after his electric start, Chisholm remains one of the more exciting young players in the Majors. He entered Sunday as one of just seven infielders with double-digit home runs and stolen bases this season. The others: Fernando Tatis Jr., Trea Turner, Javier Báez, Ozzie Albies, Trevor Story and Bo Bichette.

Cooper, meanwhile, leads the team with an .845 OPS. He's been on a tear since returning from a lumbar strain on June 25, hitting .400 with seven extra-base hits (including four home runs) and a 1.230 OPS in 19 games.

“Those are two staples in the lineup,” said Adam Duvall, who hit his 20th homer of the season to cap a four-run third inning. “You don't ever want to see anybody go down, so to have two of those in that game, that's obviously tough as a team. Obviously, we need those guys and I'm hoping that they'll be back soon.”

The injuries came in the same game that the Marlins were already compensating for the loss of Pablo López. The right-hander, who was originally scheduled to start Sunday's series finale, sustained a right rotator cuff strain while playing long toss on Friday. Braxton Garrett started in his place, allowing three runs (two earned) over 4 1/3 innings, while also igniting the club's four-run rally against All-Star Zack Wheeler with a one-out single -- his first career hit.

As for Chisholm, he burst onto the scene to start the 2021 campaign, posting a .926 OPS in April. He was also the only player in the Majors with at least four homers and seven stolen bases in the season's opening month.

Chisholm then missed 16 games from April 28-May 15 due to a strained left hamstring. He returned for eight games before sustaining a mild right ankle sprain that sidelined him for another four contests. The 23-year-old had played in 41 consecutive games since, though he was hitting .228 with a .700 OPS in those games, while going just 2-for-6 on steal attempts.

He insisted those numbers were going to once again take off following the All-Star break.

"Sky's the limit. We haven't touched where he can go," Mattingly said coming out of the break. "The fact that he's promising a better second half doesn't surprise me at all. ... Jazz is really just a world of talent that is still untapped, for me, from the standpoint that he has the chance to continuously get better."

The Marlins are just hoping they won’t have to wait too long to see Chisholm continue on that quest.