It'll be somewhat less "bright" in terms of aroma qualities and the diastatic power may have dropped. I generally recommend to people that they should use their grains within three weeks of crushing for best results, unless they freeze them in moisture-barrier bags. That said, I have brewed a partial mash beer with grains that had been sitting crushed at room temperature for two months, and it still made a decent beer.
What type of beer is it? If it's heavy on roast, I'd say go for it. If it's light in malt character, ditto. If it's a malt-forward beer that depends on a complex balance of malt character, I'd say buy new grain.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Planned: sLambic II, Flanders Red II
Primary: Fat Man Porter, Orange Blossom Mead, sLambic I
Secondary: Flanders Red I
Kegged: 3 different ciders, Janet's Brown, Barrel-aged Stout, Hallertau Blanc Pale Ale
Bottled: Flanders Red I