The injury was sustained during the Saints’ preseason friendly with Widnes, and it remains unclear as to when Smith will return.
“Matty has broke his leg and surgically had it repaired,” Cunningham said, according to Rugbyleague.com.
“It could be better but out of a bad job it’s probably the best outcome for us. It’s a clean break.
“We’ll give him four weeks and then get him re-x-rayed and re-assessed and we’ll hopefully get a time frame of where we’re at then.
“It’s hard to put a time on it because you don’t know how he’s going to respond to things.
“When you surgically fix things, you’ve got plates and nuts and bolts and all the things that can have an influence on how he recovers.
“The shorter time the better for us.”