La'el Collins will begin serving his five-game suspension Sunday, but the Dallas Cowboys right tackle is appealing the ban and said he hopes the facts of his case lead the NFL to overturn its decision.

Collins missed multiple drug tests, according to sources, but he also believes there are valid reasons for almost each missed test.

One missed test came in November on the day that Cowboys strength and conditioning coach Markus Paul died and the organization sent all its players home to allow them to grieve.

Another missed test came on the day of Collins' uncle's funeral in Arizona, according to a source. The Cowboys gave Collins permission to leave Dallas and tend to his family, the source told ESPN.

A third missed test came on the day Collins underwent hip surgery in October. The league counted a positive test for codeine against him, but Collins was prescribed the drug after having the surgery.

Collins didn't have any positive marijuana tests during the past 18 months. His representatives also have argued that under the drug policy in the new collective bargaining agreement, suspensions aren't permitted for missed tests.

If his suspension is not reduced or overturned, Collins will be eligible to return to the roster Oct. 18, the day after the Cowboys play the New England Patriots.

The suspension will cost Collins roughly $2 million and, per the CBA, voids the injury guarantee worth $6.48 million in his 2022 salary.

Collins has started 62 of the 63 games he has played for the Cowboys since 2015 at left guard or right tackle. He missed 13 games in 2016 because of a toe injury and all of last season because of the hip surgery.

ESPN's Todd Archer contributed to this report.