The midfielder pulled up in the second-half in the 2-2 draw against Bromley last Saturday and had to come off.
The 22-year-old was sent for a scan and the club received the bad news yesterday.
“It is looking like mid-November at the earliest,” manager James Rowe said at Friday’s pre-match press conference ahead of the trip to Dover Athletic.
"It is not a good injury but it was not a full rupture which is the positive but it is still a blow to the lad because he has worked so hard in pre-season and he has played a big part in our results and performances so far.
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"These setbacks and bumps in the road happen and sometimes you come back stronger from it.
"He is in safe hands and with his worth ethic I am sure he can come back a better player.”
Clarke finished last season in promising form and the former Aston Villa youngster was looking bright at the start of this campaign.
He joins Akwasi Asante, Tom Denton and Haydn Hollis on the injury list.
"It was not as if he was overloaded, he did not play on Monday, he came off the bench at King’s Lynn, it is an unexpected one but muscle injuries happen,” Rowe added.
"We have just got to be positive for the lad and make sure the environment is right for him to recover and we go from there.”