"Without having an official no-trade clause in his contract, Favre has an unofficial no-trade clause in the leverage he has.

If the Packers agree to trade Favre to any team, the quarterback can veto the deal simply by declining to report. Then Favre's rights would revert back to Green Bay, which would be forced to take him back along with his $12 million base salary -- or release him."

Basically, Green Bay has to keep him or trade him for less than market value to whatever team he chooses. Favre is looking more and more likely to end up as the starter in Green Bay.