Allen, 27, hasn't played football since 2016 when he was with the Ducks. He put his football career on hold to pursue track and field and has done quite well in that pursuit, finishing fifth and fourth in the 110-meter hurdles in the past two Olympics.
Allen caught the attention of scouts at Oregon's pro day earlier this month when he ran an unofficial 4.35-second 40-yard dash. That led to a visit with the Eagles and then eventually a three-year deal, which is a standard contract for undrafted free agents.
He suffered a pair of knee injuries at Oregon and appeared in a total of nine games over his final two seasons. His first year at Oregon was his best, as he had 41 receptions for 684 yards and seven touchdowns while averaging 16.7 yards per catch.
A three-time national champion in the 110-meter hurdles, Allen told reporters at Oregon's pro day that he intends to compete at the USA Track & Field Outdoor Championships in June and the World Athletics Championships in July before turning his attention to football.
"I'm going to put football on the back burner for now," he said, via the Oregonian. "I wanted to come to pro day and announce that I'm taking this seriously. The goal is to get ready for Worlds, compete at Worlds, win, break the world record, and then July 18th when Worlds is done, go to camp the next week."