Now the Vikings look even more vulnerable than they did before Favre returned, and they've GOT #4 there.
Favre and Rice were both injured in last year's NFC Championship loss vs. the New Orleans Saints. Rice opted against offseason surgery. He's been on the Physically Unable to Perform list this offseason, and running drills and routes on the sideline, unable to go full speed because he "feels a little pain".
He finally decided to have the surgery, which will keep him out through the first six weeks of the regular season. Fellow wideout Percy Harvin is suffering from a scary spell which is believed to be related to his migraines and although he's a threat to be a big-time contributor when healthy, nobody knows how healthy he will be at any given snap. The Vikings are left with a familiar face for Favre... but an unfamiliar face to the league the past few years, in Javon Walker. It's not a foregone conclusion, but the odds highly favor Rice and Harvin are both significantly better than Walker.
Sorry Adrian Peterson, but it looks like you're going to have to be the workload for the Vikings, because the passing game really isn't going to exist.