The 21-year-old, known as "Fizz", created a sensation with 26 wickets in his first nine one-day internationals. He burst onto the international scene in 2015 with back-to-back five-wicket hauls against India.
But surgery on his left shoulder last year forced a lengthy layoff and raised worries about his future after he took just 13 wickets in 18 international since returning.
At the Champions Trophy in England this summer, Mustafizur managed only one wicket in four matches even though Bangladesh reached the semi-finals against India.
"I noticed he was falling away a little bit in England. We have been trying to get him to be more upright and balanced so that he can pull through," Walsh told reporters.
"We are also trying to get back his pace to where it used to be and get him a little bit closer to the stumps.
"He knows what needs to be done as well. I have to give him credit because he is eager to get out there and practise."
The Caribbean great, who joined the Bangladesh coaching team last September, said he did not want to change Mustafizur's bowling action.
"I wouldn't say he will have a new bowling action but we are trying to get him more balanced at the crease and get him a bit closer to the stumps," he said.
"Last couple of days, he has been close to what he used to be. He is heading in the right direction."
Australia are scheduled to start a two-Test Bangladesh tour next month and Mustafizur is expected to spearhead the hosts' pace attack.
However Australia's senior players have voted to boycott the tour unless a long-running pay dispute with Cricket Australia is settled.
Australia cricket teamBangladesh cricket teamBangladesh vs Australia 2017Courtney Walshmustafizur rahman
First Published: July 25, 2017, 7:18 PM IST