A series of injuries have limited Walker's opportunities and he underwent neck surgery over the summer, but the Scotland international showed up well as a replacement in last weekend's win over Dragons.
Franco Smith says that while he hopes the injuries are in the past, he wants to keep the prop's feet on the ground.
He told Scotland Rugby News: "The main conversation between me and him was to keep expectations at bay.
"I think he started off playing at a high level when he wasn't physically ready for the challenge yet and I think that led to some of the injuries.
"Now he's had a chance to physically improve and become so much stronger, and he's a much better age profile now for a tighthead in this competition.
"I hope that the medical side of things are now in place and that he's physically best prepared to continue on the journey now."
During the early part of his career Walker shifted between loosehead and tighthead, but Smith wants him to focus on the latter role for the time being.
"I've only used Murphy really in case of emergency on the loosehead," he continued.
"I definitely also feel until he gets all his strength back, his ability must be in the tighthead side, and to make sure that he's also rugby conditioned now with game time in that specific role."
Smith said the improvements have been noticeable both physically and mentally over Walker's long injury lay-off.
"I believe he's mentally much stronger," he said.
"He matured as a person. He's dealt with adversity, he's come back from injury and he's been under the knife.
"I'm sure that he's much stronger, definitely much fitter and much more mentally tough than he's ever been."