FRISCO, Texas -- Try as they might, the Dallas Cowboys could not win a game without Tony Romo from 2013 to '15.
They lost their winner-take-all season finale in 2013 two days after Romo had back surgery. They lost to the Arizona Cardinals in 2014 with Romo out because of two transverse process fractures. They won only one of 12 games without Romo in 2015 after he broke his collarbone twice.
Sean Lee is turning into the Romo of the Cowboys' defense.
Without Lee, the defense can't get the job done.
Since he missed the 2014 season because of a torn anterior cruciate ligament, the Cowboys have lost five in a row without Lee, dating to 2015 and including their past two games.
The good news for the Cowboys is he should return for Sunday's game against the San Francisco 49ers.
In the three games with Lee, the defense has given up 20.6 points per game and 4.7 yards per play. In the two games without him, it has given up 31.5 points per game (not including an interception return for a score) and 6 yards per play.
"He's our best player on defense," linebacker Anthony Hitchens said. "And everyone knows that. Whenever you don't have your best player out there, I mean there's no excuses for us, but it would help if we had Sean out there playing. That's just being real. He's our best player on defense and he makes our defense better."
Lee's value goes beyond just his ability to make plays. He gets players lined up in the correct spots if there is confusion. He is a calming influence in chaotic situations. And if Lee can't get everybody lined up in time or make sure everybody is on the same page, he can invariably make the play.
"Obviously a very, very productive player for us, very good against the run, very good against the pass. He's always around the ball," coach Jason Garrett said. "I think another area where he contributes is he's just a natural leader. Guys respond to him emotionally but also just technically when you're out on the field getting guys lined up. He's got great command of our defensive system. He's got great recognition of what opposing offenses are doing. So again, just his force when the play starts, but his presence in and around that is also significant to our team."
Lee missed two games in 2015, one because of a concussion (Tampa Bay Buccaneers) and another because of a hamstring injury (Washington Redskins). The Cowboys lost both games. He was held out of last year's season finale against the Philadelphia Eagles as a precaution, similar to the decision with running back Ezekiel Elliott, and the Cowboys lost, 27-13.
The Cowboys have given up 30 or more points in back-to-back games for the first time since Weeks 14 and 15 of the 2013 season. Lee suffered a neck injury in the 45-28 loss to the Chicago Bears that season, and he did not play the next week against the Green Bay Packers in which Matt Flynn lit up the defense in a 37-36 win.
The most notable area where Lee has been missed is in the run game. With Lee, the Cowboys are giving up 87.3 yards per game, and that includes a 118-yard effort by the Denver Broncos' C.J. Anderson, which Lee called the worst tackling effort he has had in his career.
In the two games without Lee, they are givnng up 164 yards per game on the ground with Todd Gurley of the Los Angeles Rams and Aaron Jones of the Packers each going for more than 100 yards. With Lee, the Cowboys have given up four runs of 10 yards or more. Without Lee, they have given up 14 runs of 10 yards or more.
"He's a captain and he's an All-Pro player," defensive coordinator Rod Marinelli said. "But it's not just the plays he makes. It's his presence and his preparation. I think it brings a ton to us."
Lee appears ready. While working a tackling technique drill during the individual drills in Wednesday's open portion of practice to the media, Lee hit Justin March-Lillard so hard the new linebacker went to the ground.
Lee immediately apologized.
"Sean gets one of those a week," Hitchens said. "That's why he's good. He plays everything like game speed, so in order to get a game rep you've got to simulate practice as close as you can. Sometimes guys jump when you tackle them or you just finish them. But we're all just trying to get ready for a game. It's all respect. It's not him being an a--h--- or nothing. He's just ready. He's anxious. I can't wait to get back out there with him."