Eddie Royal caught a pass, landed hard on his back and left Chargers Park in an ambulance on Saturday after experiencing shortness of breath.
Trainers were walking with Royal toward the team's locker room and training room when Royal stopped and went to the ground.
Trainers then worked on Royal as Mike McCoy, Tom Telesco and Philip Rivers came over to check on him.
Several minutes later, an ambulance came on to the field. Royal was placed on a board and into the ambulance, partially upright.
McCoy said Royal had a hard time breathing, and will be evaluated further at a hospital.
On his final play of practice Saturday, Royal jumped high and snagged a Philip Rivers pass -- then came down hard.
Royal made the catch in front of safety Eric Weddle.
"Phenomenal catch," Weddle said. "He was about 10 feet in the air. He just fell straight down on his back.
"Hopefully, he'll be OK. He's tough."
Said Rivers: "When a guy gets carried off in an ambulance, you just want him to be healthy, be OK, all football aside. And hopefully that's the report we'll get back soon on Eddie."
Royal had been having a strong camp, making all the practices and appearing in both exhibition games.
For the team's receiving corps, it was another blow. Earlier this month, Danario Alexander suffered a season-ending knee injury, and Malcom Floyd went down with a strained knee. Royal has been working with the first team.