A source tells KSTP that Minnesota Vikings quarterback Matt Cassel has decided to void his contract for the upcoming NFL season, flexing an option that was written into the deal that he signed when joining the Vikings before the 2013 season.

An official decision doesn't have to be announced until Friday, however if he does opt-out, he will become an unrestricted free agent. This will leave Cassel free to look to other teams for a deal, but this doesn't rule out his return to Minnesota next season. If Cassel does explore free agency, the Vikings are open to explore a new deal with the veteran quarterback.

If Cassel does indeed hit the free agency market, he may be doing this for one of two reasons. The first of those reasons is to look for a more promising and longer-term starting role with another team. It is no secret that the Vikings are exploring options for a quarterback in this year's NFL Draft, and Cassel is largely regarded as a stop-gap solution that would likely serve as a starter for at most the duration of the 2014 season.

The other reason Cassel may be looking to hit free agency is to assess his value and look for a better contract with Minnesota than the $3.7 million he was due for the 2014 season. At 31 years old, Cassel has something left in the tank, but faces competition from some other familiar names. He will be in a quarterback market that will also feature names like Mike Vick (who is currently at the end of his deal with the Eagles) and Josh McCown, who performed incredibly in place of the injured Jay Cutler this season for the Bears.

Bleacher Report has Cassel ranked number 7 overall in the list of free agent quarterbacks this season, falling behind Vick, McCown, and even his 2013 teammate Josh Freeman. Freeman is also at the end of his one-year deal with the Vikings this offseason, and his return to the team is doubtful after a dismal performance in his Vikings debut on Monday Night Football against the New York Giants.