What happened to make Mathis think twice about holding out?
"I didn't want to have a negative impact on the team," he said. "I didn't want to send the wrong message to players, coaches, fans. I think I'm doing the right thing."
Mathis still has 3 years left on the 5-year, $25 million contract he signed with the Eagles in March 2012. He has a $5.15 million base salary this year, which is the seventh-highest base among the NFL's interior linemen, behind only the Browns' Alex Mack ($10 million), the Saints' Jahri Evans ($6.8 million) and Ben Grubbs ($6.0 million), the Titans' Andy Levitre ($6.5 million), the Patriots' Logan Mankins ($6.25 million) and the Ravens' Marshal Yoda ($5.5 million).
But he was a first-team All-Pro selection last season and none of the money in the remaining 3 years on his deal is guaranteed. There are 32 interior linemen in the league who have contracts with more guaranteed money than Mathis. If he were to suffer a serious injury this season, there's a very good chance he would never see the $11.5 million he's scheduled to receive in 2015-16.
Rosenhaus has had several conversations with the Eagles about restructuring his client's deal. But the team is wary of redoing a deal that still has 3 of the 5 years on it left to run.
"It was easy for me to sit there and think about [holding out] a month ago," Mathis said. "But when it was getting closer to the wire, it was just not something I could see myself doing.
"For multiple reasons. When I was in elementary school and got sick, I felt bad because I was behind. This isn't the kind of stuff you want to get behind on."
Holding out is a risky business. Players under contract who are AWOL from training camp are fined a league-mandated $30,000 a day. But Mathis said that had no bearing on his decision to report.
"[The fines] would be a gamble you would be willing to take if you were to hold out," he said. "The fines had nothing to do with it. I wasn't scared of the fines. It was what I'd be doing to my teammates and coaches. That's the ultimate reason [I reported]."
Mathis acknowledged that the recent suspension of right tackle Lane Johnson, who will miss the first four games of the season for violating the league's policy on performance-enhancing drugs, gave him considerable holdout leverage. The Eagles don't have a lot of experienced offensive line depth beyond Allen Barbre, who is expected to replace Johnson.
"It gave me a lot of leverage to hold out," he said. "But again, I just would feel wrong putting my team in that situation.
"I'm not trying to strong-arm the team. I'm not trying to put them in a bad situation to get what I want. I'm trying to do the right thing. I'm not really worried about it. Hopefully, it works out. If it doesn't, I'm still going to be the same football player."
Three years ago, wide receiver DeSean Jackson was unhappy with his contract situation and let that unhappiness fester and affect the way he played. Mathis said that won't happen with him.
"I'm able to put anything on the back burner when it comes to playing football," he said. "I've dealt with a lot of stuff in my career, and I've always been able to block it out and focus on the game.
"Focus is a huge part of this game. You've got to be focused at all times during the game. I used to let stuff creep into my mind, overthink things. Now, I simplify it, focus on the task at hand and not think about anything else."
Safety Keelan Johnson has been excused from camp for an undetermined amount of time to deal with his recent arrest in Arizona. Johnson was arrested last week for an altercation with police at a bar in Tempe. He was charged with assaulting a police officer, passively resisting arrest and disorderly conduct. Johnson, who played at Arizona State in Tempe, played in two games for the Eagles last season and spent the rest of the year on the team's practice squad. He met with Chip Kelly on Thursday. Johnson will count against the Eagles' 90-man roster limit while he's away.
Jeremy Maclin, who missed all of last season after tearing his right ACL early in training camp, said his knee is fine and he's ready to pick up where he left off before the injury.
"I'm just excited to play football again," he said. "I had to watch last year from the couch and sideline. That wasn't very much fun for me. I'm looking forward to going out there and playing again."
Maclin, who was the 19th overall pick in the 2009 draft, had 258 receptions and 26 touchdown catches in his first four seasons with the Eagles before last summer's knee injury. He still is looking for his first 1,000-yard season.
"As far as numbers, I've never really gotten into numbers," he said. "But if they plan on me being a big part of this offense like I think they are, the numbers will come."
Despite the injury, the Eagles signed him to a 1-year, $5.25 million contract in February.
"Not many people come off an ACL injury and get a 1-year deal up to $6 million," Maclin said. "It just doesn't happen."