Not only should he feel like walking to the surgery, I would positively encourage it. Very unlikely that his treatment would affect a thing like that. As to how he feels, only you can judge.
It happened that on Wednesday past, I had my 12 weekly Zoladex jab at my GP's practice in Leicestershire at 9.30, then my Chemo session at 11.30 in Coventry, a 45 minute drive away. No interaction between the two events at all, even if they'd been t'other way round. But, but....
Do bear in mind that the low points for white blood cells are the middle week, ie, 22-29 March in your case. Potentially infectious folk (GP's waiting rooms a prime example)) should be avoided.
AC