Dallas Cowboys six-time All-Pro guard and team captain Zack Martin, who has been unhappy about the team's lack of interest in restructuring his contract, did not report for the start of training camp, a source told ESPN's Adam Schefter on Tuesday.

Martin is scheduled to make about $7 million less this season than the NFL's top-paid guards. Chris Lindstrom of the Falcons and Quenton Nelson of the Colts are at the top of that list this season at an average of $20 million.

Last season marked a sixth first-team All-Pro nod for Martin, who at age 32 is among the most productive players at any position.

He gave up three sacks on a 96% pass block win rate, the eighth-best clip in the league. His 73.8% run block win rate was also impressive.

The Cowboys and Martin's representatives had brief discussions at the NFL combine in February about reworking the seven-year, $93.41 million deal he signed in 2018, according to sources.

In March, the Cowboys restructured Martin's contract for the fifth straight year to help create cap space, turning nearly $12 million of his $13.5 million base salary into signing bonus. Martin is signed through 2024. As a result of all of the restructurings, Martin's cap figure next year tops $23 million.

The Cowboys are hopeful of signing two other Pro Bowlers, wide receiver CeeDee Lamb and cornerback Trevon Diggs, to contract extensions this summer. They also would like to extend the deal for right tackle Terence Steele, who is coming off a major knee injury.

Martin, who has missed just eight games in his career, has been named to the Pro Bowl eight times. The only guard with more Pro Bowl appearances in team history is Hall of Famer Larry Allen (nine).

ESPN's Todd Archer contributed to this report.