Coach Ken Whisenhunt called the diagnosis "good news," considering Skelton had to be carted off the field in the fourth quarter of Sunday's 20-16 victory over Seattle.
Tests were negative for a fracture and initial concerns were that it was a high ankle sprain, an injury more serious than a low ankle sprain.
Whisenhunt would not speculate on how long Skelton would be sidelined.
"We don't think it's going to be something that will hold him out too long," Whisenhunt said, according to the Arizona Republic.
Kevin Kolb replaced Skelton and led the team on the winning touchdown drive. Arizona plays at New England next Sunday.
Whisenhunt was asked if Skelton is assured of regaining his starting job when he returns from his injury.
"I don't even know why that would be a question," he said, according to the Arizona Republic. "I mean, I can't look into the future and say what's going to happen six weeks from now. I can only tell you that we'll see what happens with John and how quickly he gets back, health-wise."
Information from The Associated Press was used in this report.