The Master hadn't intended to go this far, he was just angry, but didn't want to drive him to regenration. He knew he could help him even if not as medically skilled.
"Doctor...," He then gives up one of his regenrations to heal him enough so he doesn't need to regenrate. He doesn't care if he gives it up as barely seems to care about his own life.
Knows the Doctor is still injured but will be in pain. He gives him some medicine to help, but knows its strong and may upset the Doctor stomach. He lifted him and walked till he found the TARDIS. He unlocked it with the Doctors key and puts him in bed.