The West Ham midfielder has been sidelined for more than a month with a groin problem and Zola is not sure how much longer the recovery process will take.
The Hammers manager hopes that surgery will not be required and has praised his player's hard-working attitude during a difficult period.
"I don't know if he will play again this season to be honest," said Zola.
"He is working very hard on his fitness so that he can play again this season but it is unsure whether he can."
Zola had a similar injury during his playing career and he has offered Parker advice on how to manage it.
He is keen to have Parker available again as the 28-year-old has been has been in excellent form for much of the season.
Disappointing"The problem is he has a chronic inflammation in the groin and this has caused him problems, it is as simple as that," Zola explained.
"I have had the same problem he has now many years ago. It is tough because one day you feel okay and the day after you feel bad.
"Then maybe in five or six days it might be better. I am not worried and I am sure he will get over this. I'm just a bit disappointed as he's one of our key players and obviously to be missing him at this part of the season is no good for us."
Zola is confident Parker will eventually overcome the problem and be able to continue his career as normal.
"Once I sorted it out I never had problems again with that," he said.
"I gave Scott all my knowledge about it, but everyone is taking care of him. You have to be patient and keep working until he gets over it."