http://msn.foxsports.com/nfl/story/6043160 Peterson tore a pectoral muscle early in the 41-0 victory against the New York Jets on Sunday. Tests Monday determined the severity of the injury. Coach Jack Del Rio said Peterson likely will get a second opinion, but he was confident Peterson will be place on injured reserve. "It's unfortunate," Del Rio said. "Mike is obviously a very good football player and a very spirited leader. He brings a lot of energy, a lot of temperament. He worked really hard to have a big year for us. He's played well in the middle for us since we got here in '03. That's a blow. It's another blow for us to overcome. "The way we approach it is we prepare our guys to be able to step up and fill the gap. We expect guys to play well around them and we continue on our quest." Peterson started every game the last three seasons for the Jaguars, making 535 tackles, 12 sacks, six interceptions and four forced fumbles. He started all five games this year and had a team-high 42 tackles, an interception and two quarterback pressures.