It's been known for some time now that Jon Favreau was interested in directing The Avengers should his schedule allow it. When the film's release date was pushed to May 4th, 2012, lots of folks figured the move was done, in part, to allow time for Favs to come in and helm. Earlier in the year, a Marvel spy told AICN the following: "Avengers is delayed a year because of financing issues but also because the plan is for Favreau to helm it. Everybody here loves the guy and he wants to do it, but it would have been impossible for him to do before the date change given his Iron Man 2 commitments. Also partly the reason why he agreed to do the Stark sequel on such an accelerated schedule was so he could get given first dibs on this. It would still be a punishing schedule for him, so hes not firmly confirmed yet, but he is certainly the presumptive director at this point."
Since then, though, it appears things have changed. Favreau will re-team with Robert Downey Jr. following their work on Iron Man 2 as director on Cowboys & Aliens, and he now tells MTV that he won't also be directing The Avengers because schedules just don't work out. Instead, he says he's going to executive produce: "They'll have to [find a different director], because I'm not going to be available", said Favreau. "It's something I'm being the executive producer on, so I'll definitely have input and a say."