Essendon star Dyson Heppell and St Kilda young gun Jack Billings are the latest players to be sidelined as the AFL pre-season injury toll continues to grow.

Heppell experienced knee soreness at training and underwent minor surgery on Tuesday, while Billings will miss up to a month after straining his right hamstring in the Saints’ NAB Challenge opener against Brisbane.

“Dyson will have an arthroscopy to remove a small piece of cartilage which had become a loose body,” club doctor Bruce Reid told Essendon’s website.

“Julian Feller will operate on Dyson this morning and we expect he’ll be back training in two weeks’ time.”

Heppell, 22, is coming off a brilliant season where he took out the club’s best-and-fairest award and was named All-Australian for the first time.

St Kilda have big plans for Billings, who added six kilograms of muscle to his frame after an impressive debut season.

“Unfortunately I gave it a bit of a strain early on in the game – it was about two or three minutes in,” Billings told the club’s website.

“Obviously we’ll just have to see how the hammy responds … but fingers crossed I’ll hopefully be available for the start of the season.”

The Saints will take a conservative approach with the 2013 No.3 draft pick, who suffered a strain in the same hamstring late last season.

The pair join a long injury list across the league soon after the start of the NAB Challenge.

In the last month, Melbourne’s No.2 draft pick Christian Petracca, West Coast defender Eric Mackenzie and Western Bulldogs midfielder Tom Liberatore have all needed season-ending knee reconstructions.

Adelaide veteran Brent Reilly also suffered a skull fracture in a sickening training accident.