Williams was a try-scorer in Ulster's Heineken Cup Round Five win over Glasgow Warriors on Friday, before being substituted in the 62nd minute.
The former Blues and Aironi number eight has been in impressive form this season for the Irish side, with seven tries including three in his last three matches.
Outhalf Paddy Jackson was assessed on Sunday for an ankle injury he picked up against Glasgow, as was winger Craig Gilroy who suffered a bang to the head on Friday night.
Jackson's ankle is responding well to physiotherapy treatment, while Gilroy is following the necessary return-to-play protocol.
It is hoped that both players will be available for selection for this weekend's Heineken Cup game against Castres Olympique.
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.
