Earls suffered the injury in Friday's RaboDirect Pro12 defeat to Leinster at the Aviva Stadium - with scans subsequently revealing the extent of the problem.
The 24-year-old will now miss the Heineken Cup meetings with Northampton and Castres as well as the league meetings against Edinburgh and the Ospreys.
Earls is also a doubt for the European double-header against the Scarlets next month.
A statement from Munster read: "Keith Earls had a scan yesterday in Limerick that confirmed he has sustained medial ligament damage and will be out of action for four to six weeks."
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.
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Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
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The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
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The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
