Mark Sanchez fumbled part of his credibility in the NFL free-agent market Friday.

The former Jets quarterback was suspended for the first four games of the 2018 regular season for violating the league’s performance-enhancing drug policy. Sanchez has yet to find a new team after serving as the Bears’ third-stringer on a one-year deal last season.

Sanchez, who has bounced around four teams after spending his first four seasons with the Jets, said he was stunned when the NFL informed him of his positive test.

“I was blind-sided by the news and I want to say unequivocally that I have never cheated or attempted to gain a competitive advantage by using a banned performance enhancing substance,” Sanchez said in a statement on his Instagram account. “During the past 9 years as an NFL player I have been subject to 73 drug tests — an average of over 8 tests per season — and all but one have been clean. I have taken the same regimen of supplements for the past five years without any issues.

“The timing and results of my tests establish circumstances of unknowing supplement contamination, not the use of performance enhancing substances.”

Sanchez, 31, likely will appeal the suspension. In the meantime, he will hope for a call from a team in need of a veteran quarterback who has experience mentoring young talent, like Trevor Siemian and Paxton Lynch with the Broncos, Dak Prescott with the Cowboys and Mitchell Trubisky with the Bears.

Sanchez never played like the franchise quarterback the Jets envisioned when they selected him with the No. 5 overall pick in 2009. Starting almost every game over four years, Sanchez threw more interceptions (69) than touchdowns (68).