J.J. Watt had five partially or fully torn muscles in his core area during the 2015 season.

Watt underwent surgery on both sides of his body.

Watt had partially torn left and right abdominals and a partially torn right adductor longus. He also had a fully torn left adductor longus and a fully torn left adductor pectineus, which are two of the three muscles that connect the pelvic bone to the left thigh bone.

Watt broke his hand on Dec. 9 and played three games with a club cast.

Watt didn't miss any games due to injuries.

Chip Kelly and Trent Baalke have differing opinions on why Colin Kaepernick lost his job last season as starting quarterback of the San Francisco 49ers.

“It’s not like his skill set diminished," Kelly told Denver's 9 News Tuesday. "I mean he went on injured reserve last year. He only played half the season. He was legitimately injured. He’s in the process of rehabbing right now – he had a shoulder, had a thumb, had a knee. That’s where when people look at where he fell off -- he didn’t fall off. He got hurt."

When Kaepernick went to injured reserve, Baalke claimed the injury had nothing to do with the benching.

Kaepernick suffered the shoulder injury -- a torn left labrum -- in an Oct. 4 loss to the Packers. The thumb tear came Oct. 22 against the Seahawks and the knee injury in the following game against the Rams.

Kaepernick's agents have been seeking a trade, but Kelly continues to lobby for him to remain with the 49ers.

Kelly said he's spoken regularly to Kaepernick and that the quarterback "knows I'd love to have him."

Justin Houston underwent ACL surgery in February and could miss the entire 2016 season.

The Kansas City Chiefs' trainer said the normal rehab period for such a procedure is between six and 12 months.

"We're hoping just because of his work ethic and he's been a fast healer in the past that's not the case and that he'll be able to play this season,'' Andy Reid said. "It's too early to be able to tell on that.''

Houston is one year removed from a 2014 season in which he led the NFL with 22 sacks.