After re-evaluating James Stewart's shoulder injury, the Lions decided to put on him on season-ending injured reserve Tuesday.
After injuring the shoulder in Detroit's final preseason game against the Bills, it was originally thought that Stewart would only miss the first three or four weeks of the season.
While Stewart's injury obviously hurts, Detroit addressed its lack of depth at tailback over the weekend by acquiring Olandis Gary from the Bills.
"Given the health of our situation at tailback, a trade was a possibility, so we pursued it," Lions coach Steve Mariucci said. "He gives us another veteran back on board."
Gary, 28, is entering his fifth NFL season and joined the Bills last spring as a free agent after spending his first four years with Denver.
Playing behind Clinton Portis last year, Gary managed just 147 yards rushing in 13 games, including two starts. His best season came as a rookie, when he had 1,159 yards rushing and seven touchdowns in 12 starts with the Broncos.
Stewart was entering his fourth season with the Lions. During his three seasons in Detroit, the former University of Tennesse star has twice rushed for more than 1,000 yards. For his career, Stewart has registered 1,478 carries for 5,841 yards and 48 touchdowns. Stewart, who played the first five seasons of his career with the Jacksonville Jaguars, has started in 70 of 101 appearances.
Len Pasquarelli is a senior writer for ESPN.com. Information from The Associated Press was used in this report.