RICHMOND will be without key defender David Astbury for at least a month after suffering cartilage damage to his knee in the loss to St Kilda in round four.

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Astbury landed awkwardly after a marking contest in the second quarter at Marvel Stadium last Saturday and left the ground for treatment, before playing out the game under duress.

However, scans the next day showed he had damaged the cartilage behind his kneecap.

The 29-year-old will have arthroscopic surgery to repair the injury and Tigers physical performance manager Peter Burge said he would miss up five weeks. 

"He was having a bit of an issue with landing and hopping. But we got him back out there and he was able to function for the rest of the game," Burge told the club's website.

"He had some scans on Sunday and there’s a little bit of loose fragment of articular cartilage which had come off behind the patella which needs to be removed. 

"So he's going into surgery today (Tuesday) and will probably miss around 4-5 weeks."

In better news, utility Josh Caddy will be available for Sunday's clash against Melbourne despite suffering what Burge described as a "very minor glute strain" against the Saints.

Burge also confirmed superstar midfielder Dustin Martin had pulled up well from his first game back after recovering from rib soreness, and would face the Demons.