The 26-year-old was on the end of a nasty tackle against Solihull Moors a couple of weeks ago and had to be stretchered off.
“We have got the results back and he has ruptured lots of stuff which is not good,” assistant manager Danny Webb told the DT.
"The gaffer has given him a little bit of time off just to gather his thoughts.
"He was really flying and he is a great lad and our thoughts are with him.
"It will be a while, I don’t know if it will be a season job but it will certainly be a good few weeks yet.
"It was another horrific tackle.
"I think it makes you a little bit more sad for the lad because it is no fault of his own.
"When it is out of your hands it is a bit of a stomach-churner so it a shame for him, for us and the fans because I think they were starting to see what Jak is capable of.”
When asked if the club made a complaint against referee Lewis Smith, who did not punish the tackle on McCourt and sent off Curtis Weston in the same match, Webb replied: "You have to weigh up sometimes...what is the point in doing it? Will there be any retribution? It is done now. It is not going to make Jak’s ankle better.
"My disappointment after Solihull was that it is two weeks running that a tackle like that has gone unpunished.
"What you don’t want is for people to come to Chesterfield and think ‘we will two-foot people and we will get away with it’ and that is the thing you get a little bit angry with.
"But like I say it is done, we have got to get on with it, we have not only got to get over the speedbumps but these unfair hurdles.”
And when asked if there should be punishments for referees, Webb added: “I don’t know. We have had some good referees this year and it is a tough job. All I will say is that the two tackles which have ended lads’ seasons, potentially, have gone unpunished and I don’t think that is right.”