PITTSBURGH (AP) — Defensive end Aaron Smith, one of the Pittsburgh Steelers' best defensive players, is out for the rest of the season after he tore a biceps muscle during their 21-point loss at New England on Sunday.

Smith, an excellent run defender and one of the Steelers' most reliable players since breaking into the NFL in 1999, tried to keep playing during the 34-13 loss, but had to be replaced several times.

Coach Mike Tomlin knew that was a bad sign, and post-game tests revealed the tear. Smith apparently was not hurt on a specific play, but may have gone into the game with a partial tear that became worse as he played.

''Being the guy he is, he continued on,'' Tomlin said Tuesday. ''He came out a few times, and that was worrisome because this guy doesn't come out of games.''

Smith is used infrequently as a pass rusher in the Steelers' blitz-heavy defense, which didn't sack Patriots quarterback Tom Brady once. The 31-year-old Smith does have a fumble recovery and an interception this season, and his ability to control offensive linemen regularly leads to sacks by the Steelers' linebackers.

Smith missed most of three games with a knee injury earlier this season and was replaced by Nick Eason. Travis Kirschke is also expected to get more playing time with Smith out.

The injury is not expected to be career threatening, Tomlin said.