Skipworth, 28, picked up the injury in the third term of the Bombers' round four loss to North Melbourne and underwent MRI scans on Monday.
The Bombers are confident the injury will put Skipworth out of action for up to three weeks, but concede the break could be longer.
"We are still waiting on the results of the reports, but our medical staff are telling us it is a minimum grade one strain which will keep him out for two to three weeks," football operations manager Paul Hamilton told essendonfc.com.au.
"It just depends on how quickly he recovers. Obviously it has been less than 24 hours since the injury occurred so sometimes you need a couple more days in order to get the full view of what the outcome will be."
The former Adelaide player has been one of the success stories of the year, after been thrown a lifeline by Essendon coach Matthew Knights late last season.
The hard working midfielder spent two years in the VFL playing for the Bendigo Bombers since being delisted by the Crows in 2006.
He has played every week in Essendon seniors this year and averaged over 20 touches a game.
Hamilton said Skipworth was saddened by the fact he would miss his first opportunity to play against Collingwood on Anzac Day, but remained positive about his resurrection as an AFL player.
"He is fine with it. I spoke to him after the game on Sunday and he was naturally very disappointed because he has fought incredibly hard to get to the stage where he has played a few games," he said.
"With ANZAC Day next week, he will be disappointed from that point of view but he understands that is football too so he will work as hard as he can to recover as quickly as he can."
