I have been unable to do any serious running for 10 weeks now with a groin strain. With physio's approval I tried building mileage back up after 2 weeks to try for the London Marathon - big mistake, subsequent recovery despite regular physio sessions has been very very slow. Warning, groin strains can be very slow to recover so I really would advise that your priority must be full recovery from the injury. Don't do that race, there are other races to do, otherwise you risk a long term chronic injury.