The Australian international has been dropped for big games by manager Tony Mowbray this season despite being Celticâ€™s leading goalscorer for the past two seasons and again topping the charts this term but Walker has called for him to lead the Glasgow clubâ€™s attack.
McDonald came on as a sub late in the second half of Celticâ€™s clash with the lowly Falkirk on the weekend to net twice in seven minutes to allow the league leaders to take just one point home from a match they were widely tipped to win.
The fact that McDonald started on the bench was wrong according to Walker who is working for Sky TV as an expert analyst.
"Scott is a scorer, bottom line. In my book it would be him in the team with one other,â€ť Walker said.
"I know he missed a couple of chances last week against Hamburg (in the Europa League). But with the amount of ball Celtic get throughout the course of 90 minutes in the SPL, he should be the one who is in and around the six-yard box.
"His goals against Falkirk at the weekend proved it. He got his first with his head and that showed you do not have to be a giant to net headers if your positioning is good.
"His second was perfect as there is nothing better for a striker than timing your run for a tap-in from close range.
"I'm sure Tony (Mowbray) would like to strengthen in the striking department but that can't happen until January and, for the time being, Scott has shown himself to be fairly reliable.
"His return in terms of goals since signing for Celtic has been terrific and, if he continues to work and improve his game outside of the box, he will just get better.
"Scott possesses what I would call a 'good sniff'. He appreciates what is going on in and around the penalty area and can usually sniff out the right place to be at the right time.
"Celtic need a striker right now who can secure his fair share of goals and, more often than not, Scott has come up with the goods. I would be looking at him with a partner."