Dejagah, who signed for the Cottagers from Wolfsburg at the start of the season, has impressed fans with his pace and attacking intent but will require an operation to repair the damage suffered when he collided with an advertising hoarding.
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Since joining the west London club for a reported fee of around £2.1 million, Dejagah has yet to find the back of the net in 24 games for the club.
Jol also revealed that midfielder Eyong Enoh is a doubt for their trip to Aston Villa, where he says they need another win to ensure their Premier League place for next year.
"We will do an assessment tomorrow," Jol added. "He could probably play but we are not sure yet.
"I feel we need another win because you never know. Realistically we are fine but if everyone else starts winning in the last six or seven matches then you could have a problem.
"Hopefully we will get a couple of results in the next week or so. Overall we have done well away from home. There have been too many draws and even at Newcastle we could have done better. It is disappointing to concede in the 93rd minute.
"[Aston Villa] have got quality. They have [Christian] Benteke, [Gabriel] Agbonlahor, even [Darren] Bent on the bench. If you look at their results, especially at home, they are okay."