Frank Shamrock says he didn't mean to hurt the dog he tied to a truck and left at an airport ... telling TMZ Sports, "I know what I did was wrong, but there was no way out of it."
As we previously reported, the UFC legend is under investigation after cops say he abandoned a dog at Dallas Love Field Airport ... leaving it tethered to the bed of a pickup truck for 5 days.
Now, Shamrock is explaining to us why he did it ... saying, "I had no other solution to solve that problem.