The Doctor by Theodore L. Thomas (Orbit #2, 1967, as by Ted Thomas) begins with a medical doctor called Gant waking up in a cave he shares with his “wife” and son:
The barest glimmerings of dawn filtered into the cave, and the remnants of the fire glowed at the mouth. Gant went to the fire and poked it and put some chips on it and blew on them. It had been a long time since he had had such a vivid memory of his old life half a million years away. He looked at the wall of the cave, at the place where he kept his calendar, painfully scratched into the rock. It had been ten years ago today when he had stepped into that molybdenum-steel cylinder in the Bancroft Building at Pennsylvania State University. What was it he had said? “Sure, I’ll try it. You ought to have a medical doctor in it on the first trial run. You physicists could not learn anything about the physiological effects of time travel. Besides, this will make history, and I want to be in on it.” p. 8
It soon becomes apparent that he is stranded in the past with a tribe of cavemen, and we follow him during his day and see him hunt, attempt to treat various members of the tribe for their medical problems, and generally navigate life in the past with this aggressive and brutish lot (something that is accentuated by the ending).
This is an intriguing story, but it is overly compressed (it almost reads like a synopsis of a longer work) and should have been a longer story.
*** (Good, but too short).