What kind of long runs have you put in previous to this injury? You might be able to get away with taking some time off and still have a good race, if you've already put in some solid training.
I remember one year, I sustained a hip flexor injury three weeks out from a marathon; I barely ran at all during that taper, and ended up having one of my best races; I have never felt that good throughout an entire marathon and ran a huge negative split ( although that being said, I did go out on the slow side because I was nervous with that injury). It really taught me a lot about the importance of a good taper.
Injuries suck, and never more than right before a big, expensive race. Hope it works out for you!