Burger sustained the injury in the first half of the Stormers' 29-10 Super Rugby semi-final loss to the Crusaders at Newlands on Saturday.
The Stormers confirmed the injury but said it was unclear how long Burger would be sidelined until he had scans and was assessed on Monday.
Burger was hurt early on but played through until half-time. He didn't come out for the second half.
South Africa picks its squad for the away leg of the Tri-Nations next weekend, and opens the tournament against Australia on July 23. They begin their World Cup defence on September 11.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
$29.99
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
