The Welsh international centre toured New Zealand with the Lions four years ago but has since suffered a string of injuries.
The latest setback, an ankle injury that kept him out of contention for the recent Lions tour of South Africa, now looks set to prevent him from playing at the start of the new Magners League season.
Henson sustained the injury in the EDF Energy Cup semi-final against Gloucester in March and the Ospreys have confirmed that they are still unsure when the 27-year-old will be fit for selection.
"It's frustrating for Gavin as well as the region just not knowing when he's going to be fit and back on the field. We can't put any timescale on it," said new Ospreys boss Scott Johnson after Henson had not been present at a shirt launch on Tuesday.
"We are not able to put a date on when he will be back in action, we've just got to give him time and that is what we are doing," added Ospreys' elite performance director Andrew Hore.
"It is a blow. It's the final stages he can't seem to get through."