With just two matches remaining on the tour the British & Irish Lions will not call for a replacement at this stage.
Byrne said, "I am very disappointed that I got injured in training today and that my tour is over. I was recovering from my foot injury and was taking part in training when I hurt my thumb in a freak accident."
"To be ruled out of the tour at this stage with just two matches left is devastating. Returning home immediately is the right thing to do as it means I can get the right medical treatment straight away. I wish the boys all the best for the rest of the tour," added Byrne