Shelby Filbeck wrote on Facebook that Ruddick, who weighs around 90kg, was looking after his friend Katie Rigg's dog when he got "so upset" and lashed out.
"After 'loosing (sic) his cool' and hitting poor Luca he led him outside and let him run off, all alone and bleeding profusely," she wrote. "Breck told Katie that 'Luca had ran off' leaving out the part about him beating the crap out of Luca. She spent the whole night looking for her dog."
Filbeck said Rigg was reunited with Luca the next day, when someone found the canine in a carpark.
"He was then rushed over to the vet where they found that his jaw had been broken and he would need surgery," Ms Filbeck wrote.
"The next day Luca went in for surgery where it was found that his jaw bones were shattered (not just broken), he had to have 6 teeth pulled, which will be permanently gone forever and they had to keep him at the vets for two days instead of one."
Luca has been on an oatmeal diet since, but his wounds are expected to heal.
Katie Riggs told KY3 her friend's written account on Facebook was accurate, but she couldn't comment further because she was taking legal action.
This is not my dog, but this story deserves to be heard. Earlier this week one of my close friends left her adorable...
Posted by Shelby Hartzler on Friday, 23 September 2016
Ruddick reportedly denied the allegations, saying on Facebook he "punched" Luca but did not break the dog's jaw.
"The story that's getting told is way out of proportion. I didn't break the dogs the [sic] jaw nor did I let him run away," he reportedly wrote on Facebook, KY3 reports.
"I was dog sitting him and he was on my bed, I wanted him off the bed so I gave him like a tap to try and get him off but he didn't move so I gave him a little push and he bit my hand not extremely hard but enough to shock me.
"I've apologised to her and paid all the bills because I felt so bad. I don't hurt animals that's not who I am. If you don't believe about what happened to the dog I have proof of the bill that I didn't break its jaw."
A petition on Change.org calling on Missouri State University football coach Dave Steckel to permanently remove Ruddick from the team has attracted more than 7000 signatures.
"If you feel as we do, that Breck Ruddick does not deserve the privilege of representing Missouri State University's athletic program, please sign and share this petition for his immediate removal from the team," the petition says.
The Office of Student Conduct is investigating the shocking allegations.
"It's obviously very serious," athletic director Kyle Moats said. "Not only athletics, but the entire university takes it very seriously. That's why there will be an internal investigation conducted by our Student Conduct office. We'll take it from there once we find out what the findings are."
