Thomas, who won the most recent of his seven Wales caps in 2009, was treated by club medics before being transported by ambulance to Morriston Hospital in Swansea.
The 29-year-old has undergone "successful surgery" and is now in a "comfortable condition" but he will remain in hospital during his recovery.
Scarlets chief executive Mark Davies said: "All our thoughts and best wishes as Scarlets are with Rhys and his wife Paula and their family and the region will be keeping in close contact with medical teams at Morriston Hospital as to his progress but it is understood that he is comfortable and doing well.
"I am sure the whole rugby community in Wales would join with us in expressing to Rhys - all our very best wishes for a quick and comfortable recovery."
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.
