The 25-year-old right-back, who scored in Palace's 2-1 win at Chelsea a fortnight ago, suffered the injury in training.
"Unfortunately we've lost Joel Ward this week," said manager Alan Pardew
"After his great performance against Chelsea he's got injured in training and will definitely be out for three to four weeks, so that's a blow to us."
Pardew also revealed striker Marouane Chamakh, yet to appear this term due to hamstring trouble, now faces at least another three weeks on the sidelines with an abductor injury.
But there was better news ahead of Saturday's visit of Manchester City as key midfielder Yohan Capaye will be fit.
The £10million summer signing from Paris Saint-Germain came off injured during France's friendly against Portugal last week, but Pardew says he will be available to face the Barclays Premier League leaders.
"Yohan came of as a precaution, he's had problems with his groin and he felt a little bit in the scar tissue," added Pardew.
"He did the sensible thing in coming off and he has trained today (Thursday), and he was magnificent!"
With Palace flying high in second, albeit after just four games, Saturday's clash is a top-of-the-table encounter.
"It's an unusual position for us and something we probably can't sustain for a long period, but in the short term we can enjoy it," said Pardew.
"We deserve to be there after four games
It's just a shame there are another 34 to go."
Source : PA
Source: PA