According to a league source, the Cleveland Browns have placed linebacker D'Qwell Jackson on injured reserve.

Jackson has been sidelined since early August with a torn right pectoral muscle, and had been listed as "doubtful" for Sunday's game against the Baltimore Ravens after experiencing tightness during practice this week.

"If I go out there I don't want to feel anything," Jackson told the Cleveland Plain-Dealer. "At this point, it was too early."

Jackson missed the final ten games of the 2009 season after tearing the left pectoral muscle in a Week 6 loss to the Pittsburgh Steelers.

A second-round pick (34th overall) out of Maryland in 2006, Jackson has started 48 of his 49 career games, totaling 407 tackles, 3 quarterback sacks, 4 interceptions, and 11 passes defensed. Jackson's top season came in 2008, where he led the Browns in tackles for a second consecutive season with 154, and set career-highs with two quarterback sacks and 3 interceptions.

Jackson was not eligible for unrestricted free agency due to the uncapped year, and instead was tendered at the "Second Round" level, which is paying him a $1.759 million base salary this season.

To fill Jackson's spot on the active roster, the Browns have signed veteran wide receiver Sam Aiken.

Aiken (6-2, 220) caught a career-high 20 passes for 326 yards and 2 touchdowns for the New England Patriots last season, but could not crack the Patriots' 53-man roster this summer and was released on September 4.