Westbrook is the Eagles' career leader in yards from scrimmage (9,785) and ranks second in rushing yards (5,995) behind Wilbert Montgomery and third in receptions (426) behind Harold Carmichael and Pete Retzlaff.
"Brian is one of the greatest Eagles of all time and he is even a better person and leader," coach Andy Reid. "In my mind, there has not been a more versatile running back that the NFL has seen. I had a conversation with Brian this morning to let him know. This is by far the most difficult part of this job. We wanted to make this move now in order to maximize Brian's chances of landing with another NFL team."
Westbrook was selected in the third round of the 2002 draft from Division I-AA Villanova.
He posted career highs of 2,104 yards from scrimmage and 90 receptions in 2007.
Westbrook produced back-to-back 1,000-yard rushing seasons before settling for 936 in 2008 and was slowed last fall by injuries, including a series of concussions. He played eight games in 2009, carrying just 61 times.