The call of nature caused McDonald to run a slow time and may have been a factor as to why the Terrors did not sign him.
"I remember Scott when he came here on trial, I was his running partner around Camperdown Park. There was one day when he actually had to nip into the woods while we were out doing the run,” Kenneth said.
"I don't know for certain if that's what cost him the chance of signing here but it certainly caused a few laughs among the lads.
"He was a bit bigger back then and I remember that even I beat him in the race. Scott wasn't at his fittest then but since he's proved to be a really good signing for Celtic.
"Looking back, if we had maybe taken a gamble on him like Motherwell did then it would have paid off. It doesn't matter if people thought he was overweight because he scores goals, simple as that. That's all a manager really needs, so it was definitely an opportunity missed for us and Motherwell's gain."