Asomugha had no concussion symptoms, the team later said, according to Jeff McLane of the Philadelphia Inquirer.
The cornerback, signed as a free agent last year after spending his first eight seasons with the Oakland Raiders, also was left with a lacerated lip and sore neck as a result of the mid-air collision, which occurred on a pass play during a 7-on-7 drill.
Quarterback Michael Vick attempted to hit wide receiver DeSean Jackson near the left sideline, but Asomugha and Allen, a third-year safety, converged as onlooking fans gasped.
"Just one of those plays," Allen said. "It happens sometimes. His helmet went into my chest, and my forearm caught him a little bit. It happened so fast, it's hard to tell what hit what."
Allen remained on the ground for a few minutes, coughing. But ultimately he was able to continue practicing.
"I felt fine," he said. "I just had to get myself back together. As soon as it happened, it knocked the wind out of me and I laid there a little bit, and kind of felt around and made sure everything was in one piece."
Asomugha remained face-down and motionless as team trainers came to his aid and several teammates knelt around him.
An Eagles spokesman said Asomugha never lost consciousness, but it was several minutes before he was able to regain his feet. He then made his way to a nearby cart and was driven to a fieldhouse adjacent to the practice field, where he was evaluated.
The Associated Press contributed to this report.