"I'd imagine he's going to miss a week, possibly a fortnight if it's just a spasm.
"If it's a pull, it's three or four weeks. It's a body blow to the lad," Malpas said.
Swindon have a number of injury troubles ahead of the League One campaign.
Captain Hasney Aljofree's ankle problem is expected to keep him from training for a least another week.
Surprise return
Star striker Simon Cox also missed Saturday's 4-1 victory at Chippenham after having an operation on a broken bone in his hand, although he is expected to be fit to face Tranmere on 9 August.
There is better news regarding forward Lee Peacock, who returned to the starting line-up at Hardenhuish Park after an Achilles injury.
Malpas said his fellow Scot's return was a surprise.
"Lee only came back to training on Thursday morning and our plan was to give him a decent week.
"I thought the youth team was training today and he was going there, but they went to play a game against Cardiff.
"It's ball work that he needs, so we thought we'd bring him here and play him for half an hour.
"He felt comfortable after it, so he'll play a bit longer on Tuesday against Cardiff."
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