|ESPN.com: NFL||[Print without images]|
Hallen, 31, left the team on his own earlier this week, citing back problems. His absence, coach Romeo Crennel said at the time, was not excused.
The (Cleveland) Plain Dealer first reported Hallen's intentions, and then league and team sources confirmed them for ESPN.com.
Tests conducted by his own doctor, a West Coast specialist, apparently revealed that Hallen has a pair of herniated discs and that he also suffers from a condition known as stenosis, which is essentially an abnormally narrow spinal column.
Browns officials have not commented on Hallen's physical condition. When he left camp, Crennel said generically that Hallen had "medical and personal issues."
There have been indications for the last several days that Hallen was considering retirement.
Hallen's abrupt departure left the Browns without an experienced center. The team signed Bentley, a two-time Pro Bowl performer for the New Orleans Saints, at the outset of the unrestricted free agency period.
The acquisition of Bentley was one of the biggest signings of the offseason, and the former Ohio State star was regarded as the centerpiece of a refurbished offensive line before his injury.
Cleveland traded for New England backup Ross Tucker on Tuesday and he will compete with Alonzo Ephraim for the starting job. Tucker has 24 starts in his career and Ephraim has five.
Ephraim started in Thursday night's preseason opener for the Browns. Hallen, who had only a few days of practice with his new team, was not active for the game.
A second-round pick of the Atlanta Falcons in the 1998 draft, Hallen has appeared in 86 games for his career, with 47 starts. The former Kent State standout spent four seasons with the Falcons (1998-2001), signed with San Diego as a free agent in 2002, and played the past four seasons for the Chargers.
Len Pasquarelli is a senior NFL writer for ESPN.com. To check out Len's chat archive, click here .