ESPN's Adam Schefter first reported the trade, which does not involve draft picks, per NFL Media Insider Ian Rapoport.
Chip Kelly was reluctant to devote $11.95 million in cap space to McCoy after watching the 26-year-old's production drop from 5.1 yards per carry and 10.4 yards per reception to 4.2 and 5.5, respectively.
With McCoy's role diminished and his effectiveness waning, the Eagles reached the conclusion that it was better to pull the cord a year early than a year too late.
McCoy has also told friends that he didn't always see eye-to-eye with Kelly on practice methods and scheduling, Rapoport added.
Appearing on Tuesday's edition of NFL Total Access, NFL Media's LaDainian Tomlinson confirmed that McCoy's relationship with Kelly had become strained over the past year.
"I'm not really surprised about it," Tomlinson explained. "I had the chance to talk to LeSean McCoy a few weeks ago and he expressed to me that he didn't think he was going back to Philly next season. ... he just didn't think Philly was committed to him and he actually thought that Chip kind of phased him out of the offense at times last year."
In exchange for one of the NFL's best playmakers, Kelly is reunited with the former Oregon star Alonso, who is returning from ACL surgery on the heels of an outstanding rookie season.
After winning the power struggle for football operations in Philadelphia, Kelly is putting his stamp on the roster, unloading his rushing leader one year after jettisoning his top receiver.
If Kelly believes his system is more valuable than the marquee players he inherited, he now has eight former Ducks around which to build a contender.
Is Marcus Mariota the next Oregon-related blockbuster on Kelly's agenda?