1:38 PM PT -- TMZ Sports has learned Zelda is doing just fine after the incident, being taken care of by trained professionals at the SPCA of Texas.

A spokesperson for the organization tells us Zelda has received full care -- including "a ton of TLC" -- since she's been in their custody ... and is expected to be put up for adoption within the next few days.

Ex-UFC star Frank Shamrock is reportedly being investigated by cops after he tied a dog to a truck and abandoned it for 5 DAYS at a Dallas airport earlier this month.

Shamrock had to move his ailing mother out of her Texas home -- and in the process, was forced to take control of her two dogs.

Frank tells WFAA in Dallas he was able to find a shelter for one of the dogs ... but when he couldn't find a home for Zelda, the other dog -- he tied her to a truck and left her at Love Field Airport.

Shamrock admits the act was "terrible" ... and says he ran away from the dog in tears.

But, Frank also says his actions helped keep the dog alive, saying, "Here is what I guarantee, that dog is alive and safe right now and I couldn't guarantee that before I tied that dog to the truck and left."

Police seem to disagree ... and are reportedly investigating Shamrock -- and considering levying animal cruelty charges against the fighter.

For his part, Shamrock says he'll accept responsibility for it all, saying, "They can charge me with whatever. I will show up. It is what it is. I'm not hiding in any way."

"It's an unfortunate and terrible thing. I'm an animal lover and I ran away crying."

Zelda is reportedly safe and in custody of Dallas animal control.