The centre-back has returned to Argentina to be assessed by the national side's medical team after he broke two bones in his back executing an acrobatic clearance
The centre-back suffered the injury while acrobatically clearing the ball during Newcastle's 4-2 win over Southampton at St James' Park on February 24 and has not featured for the club since.
Newcastle manager Alan Pardew confirmed the 31-year-old has returned to Argentina to be assessed by the national side’s medical team, and could be out until May.
"Colo has gone back to Argentina,” Pardew told reporters. “There's no treatment he can have, he's broken two of the bones in his back.
"We think it's going to be anything between three and seven weeks. He's gone back for a week."