A candidate \lesssim 3 M _ { Jup } extrasolar planet was recently imaged by Kalas et al .
( 2008 ) using HST/ACS at 12 ” .7 ( 96 AU ) separation from the nearby ( d = 7.7 pc ) young ( \sim 200 Myr ) A2V star Fomalhaut .
Here we report results from M-band ( 4.8 µm ) imaging of Fomalhaut on 5 Dec 2006 using the Clio IR imager on the 6.5-m MMT with the adaptive secondary mirror .
Our images are sensitive to giant planets at orbital radii comparable to the outer solar system ( \sim 5-40 AU ) .
Comparing our 5 \sigma M-band photometric limits to theoretical evolutionary tracks for substellar objects , our results rule out the existence of planets with masses > 2 M _ { Jup } from \sim 13-40 AU and objects > 13 M _ { Jup } from \sim 8-40 AU .