It’s still unclear if the Patriots will trade quarterback Ryan Mallett this offseason, but teams are still calling about Tom Brady’s backup. The Cleveland Browns and Tampa Bay Buccaneers have expressed interest in acquiring Mallett, according to a source, but a deal still appears unlikely. The main hindrance is the NFL’s collective bargaining agreement, which doesn’t allow players who were drafted in 2011 or later to restructure their contracts until they have completed three seasons. Mallett, a third-round pick in 2011, is bound by that rule. The thinking is the Patriots would like to add value to their original draft investment, which would likely call for a second-round pick in return for Mallett’s services. If the Browns or Bucs wanted to spend that much for Mallett, they’d like to have some long-term insurance. Mallett signed a four-year contract worth just south of $3 million as a rookie, so he’d be very affordable for the next two seasons, but the teams’ fear would be that he could hold them hostage without an extension in place. By the same sentiment, the Patriots don’t have to rush to trade Mallett this offseason because he is such a low-cost backup. And if they believe he’d be worth more next offseason because of that flexibility to finally extend his contract, they’d have an added incentive to keep him until then. Of course, the Patriots could take care of a weak quarterback market, both in free agency and the draft, by trading him this offseason. Plus, they could add to next month’s draft cache that only includes five picks. Mike Kafka is the only other backup quarterback on the Pats roster, but the thought is they could make a play for Matt Cassel if he is released by the Chiefs. Naturally, the Patriots would have to trade Mallett first. There is some interest in making that happen, but not enough just yet.