Seriously.
My strong suspicion is that Griezmann and his agent just want a better contract. Atleti will benefit enormously from the new La Liga TV deal. Their revenues from domestic broadcasting have been in the 40-45m euro range but starting in 2016-17 will be
rising to around 116m euro. The following year they move to the new stadium and that will improve their matchday revenues significantly.
Basically, Atleti is on the verge of a huge financial windfall that will really change the outlook for the club. Griezmann is one of their most important players, is under contract until 2020 on wages that don't reflect his quality, and probably wants his piece of the pie.
From Atleti's standpoint, selling Griezmann makes absolutely zero sense, on the field or off. They don't really need the money and its very important for them to keep building on their success of the last few years, especially as they move into the new stadium. They don't always sell out the Calderon and the new stadium has 20,000 more seats so they really need to keep putting a very high quality product on the field to try to grow attendance.
Sorry to throw cold water on all the muppets out there...