Axford can remain on the list for three to seven days. His son, Jameson, was bitten on his right foot by a rattlesnake last month while the family was in Scottsdale, Ariz., for spring training.
Jameson has been in the hospital since, and Axford left Rockies camp for a week during spring training before returning to the team.
"He's stable, but there are still a lot of issues," Axford said.
Jameson underwent an initial surgery on Monday. But doctors found a staph infection that was more serious than they expected. They removed all the tissue and skin at the spot of the bite, down to the tendon and bone.
"My wife couldn't actually even tell me on the phone because of how tough the news was for her," Axford said. "She's been by his side the entire time in the hospital. So it was difficult to hear that, but I just keep going back to the memories of how happy he was in his good moods and his good spots."
Oberg suited up for his first major league action in Sunday's game against the Chicago Cubs.
- Mike Fiammetta