Does he have deep venal thrombosis?

It's doubtful. You did say he has an infection. That is not a DVT. A DVT (or deep vein thrombosis) is a blood clot. There would not be an infection or pus with a DVT. I figure the leg doppler is to try to determine how deep the infection is into the leg. It does sound like the infection is may be spreading into the calf area. Since the doctor gave him an anti-biotic and an ointment, I think you can wait until Monday. He should probably stay off his feet and much as possible and keep his leg elevated.