The talented Ospreys centre has been heavily tipped to make Ian McGeechan's squad but his region has confirmed he suffered ligament damage to both sides of his right ankle during Saturday's EDF Energy Cup semi-final defeat to Gloucester.
With the season reaching its climax, players will be desperate to impress the Lions selectors before the team is announced on April 21. However, Henson, who toured with Sir Clive Woodward's Lions to New Zealand four years ago, will be biting his fingernails in anticipation as rivals jostle for his plane ticket.
The injury-plagued Henson suffered his latest setback when he pulled up sharply just before half-time in the 17-0 loss to the Cherry and Whites at Coventry's Ricoh Arena on the weekend.
With regards to Henson's injury, Ospreys physiotherapist Chris Towers, said: "Following a MRI scan and specialist consultation on Monday, we can confirm that Gavin has suffered damage to the ligaments on both the lateral and medial sides of his right ankle.
"Although the injury is not so severe that he will require surgery, he will require a spell of at least two weeks in a walking cast before he can start to gradually get back to normal activity.
"At this stage, in light of the nature and extent of the ligament damage, we are predicting a four-six week spell on the sidelines before Gavin will be ready for action again."