What's it like inside -- did it cut through the casing? If it's just tread damage, I wouldn't worry about it. If only a few threads of casing are cut, it's probably good for quite a while. If a lot of casing threads are cut, keep an eye on it when you pump it up -- enough casing damage will let it start to bulge and spread.

Modest casing damage can sometimes be repaired with a hot iron and Melco seam-sealing tape, the same sort of stuff used for drysuit fabric seams. It adheres to the undamaged casing around the cut, unlike a boot that simply rides between the tube and the cut but does not restrain the cut casing.