Will A Runny Nose And Mucus Cause Problems During Dental Surgery?

My son is 4 and going for general anaesthetic tomorrow to fix a small hole in his teeth. We noticed late yesterday that he suddenly has a sort of runny nose with thick yellow mucus. When he blows his nose,he breath normal and doesn t seem to bother him or obstruct his breathing with it. Will it be a problem tomorrow? Can he still get it done? What should I do? I don t want to cancel this.