The 25-year-old picked up the problem during Serbia's Davis Cup tie with USA at the weekend.
Djokovic fell and twisted his right ankle during the opening set of his encounter against Sam Querrey, but was still able to win through 7-5 6-7 6-1 6-0. However, despite having completed his match, reports have claimed that he may not feature at the tournament in Monte Carlo, which starts on Friday.
"Injuries are part of the sport and you try to avoid them as an athlete as much as you can," he said. "The nature of the injury is still to be determined. One hour, one hour and a half after the end of the match, all I can say is it doesn't look good.'
"It's swollen, and when it's swollen it's definitely not a good first sign. I'm going to do everything I can in my power to recover till that tournament. How realistic that is, I don't know what to tell you."
Depending upon the seriousness of the complaint, Djokovic could also be a doubt for next month's French Open.