The team said he has a bruised lung and was being evaluated for a concussion.
The latest injury to the wide receiving corps was the scariest.
After landing hard, Royal walked to an adjoining field, where he dropped to the ground and began receiving treatment from the team's medical staff. It appeared he was given oxygen, and also that he spit up a small amount of blood.
A few teammates came over to check on him, including quarterback Philip Rivers and fellow wideout Robert Meachem.
"I think like anything, when you're getting carried off like that you're scared," Rivers said. "You hope for the best. You hate to ever see a teammate like that get carried off."
Rookie coach Mike McCoy came over and had a look before returning to the other field.
An ambulance was driven onto the field and Royal was sitting up on the stretcher as he was loaded inside.
"He had a little bit of a hard time breathing," McCoy said. "We're going to take him to the hospital and check him out. That's all I've got right now. I can't tell you anymore. I don't know a whole lot about it."
The injury happened in the last team drill of the day.
"All you can do is pray for him, because we don't know," fellow wideout Robert Meachem said. "Unfortunately, it was a bad fall.
"It's always scary," Meachem said. "This game is a violent game. And in this game, injuries can come and go."
Meachem said all the receivers gathered after practice and said a prayer for Royal, Danario Alexander and Malcom Floyd.
Alexander is out for the season after tearing the anterior cruciate ligament in his right knee on Aug. 6. He had surgery Thursday. Floyd strained his right knee on Monday. Both were hurt after colliding with cornerback Shareece Wright.
"He landed hard," Rivers said about Royal "Hopefully, he's all right. Anytime you get carried off the field, it's not anything too, too minor. Hopefully, it's just a precaution. Hopefully, we'll get him back; most importantly get him feeling good and healthy."
Also Saturday, McCoy said defensive end Corey Liuget has a strained shoulder, but refused to give the severity or say how long he might be out. He was hurt in the first quarter of Thursday night's exhibition loss at Chicago.
"It's just a strain. I'm not a doctor so I can't tell you all that," the rookie coach said.
Rookie linebacker Manti Te'o was still wearing a walking boot on his right foot, which he hurt in the exhibition opener against Seattle on Aug. 8.
Te'o said it felt "way better than it's felt since last week. I'm making great strides."
Te'o said he doesn't know when he'll be back at practice.