“Cyst” has appeared on dog paw. Any advice?

3 yr old golden retriever. Noticed he was walking weird on a walk last night. Waiting for response from vet. Appears to have popped last night and have some blood and pus coming out of it last night. We applied warm/soapy towel to clean and stop bleeding. He doesn’t appear to be too bothered by it today but it’s certainly still there.

Does anyone have experience with this / know what we should do? Thanks!