All of the events of Better Call Saul take place before Breaking Bad, but in the later seasons of BCS we can see the plots of the 2 shows begin to converge as that is the point of a prequel. I think the doctor you refer to is in both shows- he is sort of the "go to" medical professional for injuries that must be treated privately and cannot be reported to any hospital, lest the criminal activities of the characters be exposed. There is a point at which the doctor- in Better Call Saul- decides enough is enough and tells Nacho he is not dealing with any more Cartel injuries because "this shit is too hot for me", and he never wants to see Nacho again. But later on he is made a proposal by Mike which he cannot refuse- I think there is a whole episode devoted to him and Mike and their relationship, either on Breaking Bad or BCS. And it is Mike who gets him back in the fold of being the Cartel's go to doctor for those injuries which must be treated very, very privately and under the radar. So possibly you missed that episode.