Believed to be the same facility Wallabies utility Kurtley Beale and Canterbury superstar Ben Barba attended to help deal with personal problems, the Eels said there had been no time frame put on Sandow's return to the club.
With just three weeks remaining in the regular season, it seems unlikely Sandow will be sighted again in the blue and gold until 2014.
In a statement issued by the club, the Eels said a return to the football field was not the club's main concern.
"The club's primary focus is caring for the welfare of Chris and his family both at this time and moving forward," the statement said.
"We would please ask that everyone respect the privacy of Chris and his family during this time."
Sandow has not been sighted in the NRL since being dropped following Parramatta's 50-10 defeat to Manly on July 8.