Serbian Jankovic said, "I don't think it's that bad. I didn't break anything. I have pain on it but, you know, I don't play (today), and hopefully now I can get some treatment and feel better for my next match."
In the second week of Wimbledon, the 23-year-old Jankovic held off 17-year-old Caroline Wozniacki 2-6, 6-4, 6-2 despite slipping and hyper-extending her left knee in the first set.
Battler Tamarine fought back from a set down against Marina Erakovic on Saturday to book her place in the fourth round.
She blew a chance to take the first set when she tossed away a three-game lead against the 53rd-seeded New Zealander who is ranked seven places below.
The 31-year-old Thai was 4-1 up but lost five games in a row as Erakovic claimed the first set 6-4.
Tanasugarn regained her composure and showed the kind of quality that has helped her to career wins against Amelie Mauresmo, Jennifer Capriati and Mary Pierce.
She took the next two sets 6-4 6-4.