Have you been able to look at the foot yet? Is it swollen?
If infection becomes bad, the cat may lose its leg. Best to find some help for the poor thing.
Bundle him tightly in a towel with his foot out, and soak the foot in warm salt water. (Prep the bowl of salt water first, and have it ready.) Do this for 5 or 10 minutes, and then again in about 12 hours.