Caldwell moved to Scotland to begin his professional career. Glasgow was to be the base from where Caldwell, under the management of Sammy Docherty, set out on a new era. In his first bout, a two-round stoppage of Englishman Billy Downer signalled the start of John's rise through the ranks. As Caldwell recalled, the training regime he followed required discipline, self-control and dedication. ""In Glasgow, I attended mass at half-six every morning ... fter that, I would take to the hills outside the city for the running and stamina training. I had to watch my diet and keep myself right that it was really tough going. My exercise routines were so varied and beneficial that the Glasgow Celtic manager Jimmy McGrory asked me to go along and help the team out.""