Johnson was taken by ambulance to Lehigh Valley Hospital for further evaluation, the team said. The injury occurred during seven-on-seven drills. Johnson went over the middle, tried to grab a low pass from quarterback Mike Kafka, and fell awkwardly.
"Sometimes the body falls in ways it isn't supposed to," said safety O.J. Atogwe, who held Johnson's hand as he lay on the ground.
Kafka and several Eagles players turned away after watching the injury.
"He was in a lot pain. It was as an ugly sight, as you heard the crowd 'Ooh' and 'Ahh,' " Burkholder said. "My assistant . . . did the right thing by covering it up with a towel so the kid doesn't see it."
Johnson's leg was stabilized with an air cast before he was lifted onto the back of a cart. As he was carted off the field, several players came over to offer support, and fans gave him an ovation. Johnson pointed to the sky.
He's "like a little brother to myself," Eagles receiver DeSean Jackson said. "I've been keeping him under my wing. So it definitely touches me in a tough spot."
Johnson was drafted in the sixth round by the 49ers last year but was released before the season. The Eagles added him to their practice squad, where he stayed until the final game of the season, when they added him to the 53-man roster. He did not dress for the game.
"He worked out all off-season like a wild man, and you hate seeing that," Eagles coach Andy Reid said.
The Eagles are down two receivers since the start of camp. Riley Cooper broke his left collarbone and will be sidelined for six weeks. He had surgery Monday. Reid said Sunday that he had no immediate plans to add another receiver, but the Johnson injury - likely a season-ending one - may lead to a signing.
The Eagles worked out Travis Cobb, an undrafted rookie, on Monday.
Jackson jacked up
The fisticuffs continued at camp when Jackson and Brandon Hughes mixed it up during team drills.
It was the third fight in the last two days of practice, as Reid has ratcheted up the intensity with long periods of live hitting.
"It's part of football," Jackson said. "Scuffles happen. He's not a starter. I'm a starter. As far as any of that type of stuff I don't really care. Whoever it is it is."
Hughes would not talk about the fracas.
Earlier in the practice Jackson put a move on Hughes, a third-year cornerback on the roster bubble, after he caught a short pass. Their scuffle happened away from the play. Former Eagles receiver and current coaching intern Greg Lewis held Jackson back.
"I'm a starter on this team and one of the leaders," Jackson said. "You don't want to cause anything - me getting hurt. . . . You just got to be smart with things like that."
Babin has MRI
Defensive end Jason Babin had an MRI on his calf, and it confirmed the team's original diagnosis of a strain. There is no timetable for his return, the team said, although Reid said Sunday that he could be back in a week.
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