New England Patriots wide receiver Julian Edelman is facing a four-game suspension for violating the NFL's policy on performance-enhancing substances, league sources told ESPN on Thursday.

The suspension is currently under appeal as Edelman has taken "hundreds of tests" and has not tested positive before, a source told ESPN.

If he were suspended for four games, Edelman would forfeit $470,588.20 in base salary. The Patriots' first four games are against Houston, at Jacksonville, at Detroit and home against Miami.

Edelman, who has been a regular participant in the team's offseason program, organized team activities and minicamp, is returning from an ACL tear during the 2017 preseason that forced him to miss the entire season. He turned 32 years old last month and is entering his 10th season in the NFL.

Wide receiver isn't a position at which the Patriots are loaded with experienced, quality depth. After losing Danny Amendola and Brandin Cooks this offseason, the Patriots' receiving corps consists of Jordan Matthews, Cordarrelle Patterson, Chris Hogan, Malcolm Mitchell, Kenny Britt, Phillip Dorsett and sixth-round draft pick Braxton Berrios.

While it is difficult to win appeals, the system is not infallible. Cornerback Richard Sherman won his appeal during the 2012 season while with the Seattle Seahawks.

The current policy related to performance-enhancing substances is expected to be discussed in negotiations for a new collective bargaining agreement, a source told ESPN. The current CBA runs through 2021.

Edelman, who has worked closely with Tom Brady's trainer, Alex Guerrero, at the TB12 Sports Therapy Center, previously discussed how Guerrero has helped him.

The link between them led Guerrero to issue the following statement:

"I've known Julian since his rookie year and he is a phenomenal athlete who takes his training seriously -- it's disappointing to hear today's news. Elite athletes sometimes work with multiple coaches and health professionals as part of their off-season training. Here at our facility, we take a natural, holistic, appropriate and, above all, legal approach to training and recovery for all of our clients. And anyone who would suggest otherwise is irresponsible, and just plain wrong," he said.

ESPN's Dan Graziano and Mike Reiss contributed to this report.