It's buried about 2/3 of the way down this story from Heyman. Pretty clear that this came from Scott Boras.
Honestly? I don't believe it for a second. The offer was supposedly made by Fielder 2 years ago, which means it would have come from Fielder at age 25 and allowed the Brewers to control him through age 33. Sure the price-tag was steep, and it was more years than they would have liked, but it's not all that much more money per year or all that longer than the 5 years, 100 million (rumored to be 6 years, 120 million) the Brewers acknowledge they put on the table.
What do you think? Was that offer really ever made? And if so, was Melvin right to say no? I think if it had been on the table Attanasio would have pulled the trigger, personally, and this strikes me as much more likely to be a little bit of sour grapes from Boras since the Brewers never really engaged this offseason and are, in part, one of the reasons for the slow start to Fielder's free agency, since Boras didn't have an offer to shop around.