"He could have cut them accidentally!" The Doctor might have argued further, but then he saw what the other two were staring at and, well. He didn't call himself the Doctor just for the pompous title. Without even thinking about it he crawled over to close the distance between them and he put an arm around the Master, grabbing his wrist with one hand. "Hold still, alright? Try to keep your hand as relaxed as you can."

He grabbed the hilt of the knife with his free hand, moving his fingers to make sure to hold the Master's hand steady. "I'm going to pull it out now. Are you ready?" In theory it might be wiser to wait with pulling it out until they were in the infirmary, but doctor he might be, but he was also the Doctor and he wanted the knife in his possession and the Master back under his control as fast as possible.