The Wales centre had hoped to play for the first time since the British & Irish Lions' 2nd Test in June following groin surgery in Germany but he failed a late fitness test before this Powergen Cup tie after travelling to the Memorial Ground. However Ospreys team manager Derwyn Jones is confident Henson will be fit to face Leicester in Sunday's Heineken Cup clash at Welford Road.
"Gavin picked up a back strain lifting some weights earlier in the week. He trained with us on Saturday but didn't get involved in any contact work," said Jones. "We took him with us to Bristol to give him every chance of playing but he had a fitness test at the team hotel before the game and his back was just too painful.
"We reckon he was about 24 hours from being fit so we're hopeful that he will play next week."
Meanwhile the Ospreys looked impressive enough without Henson after coming from behind three times to beat Bristol for whom wing Marco Stanojevic scored a hat-trick. New Zealand pair Damien Karauna and ex-All Black Adrian Cashmore both went over in the first half as the Ospreys led 20-14 at the break.
Then Cashmore, Steve Tandy and James Bater all went over to clinch the Ospreys' first win in the competition. However defeats to Gloucester and Bath meant they could not join Llanelli Scarlets in the semi-finals.
Tries - M Stanojevic (3), L Robinson
Cons - T Hayes (4)
Tries: A Cashmore (2), D Karauna, S Tandy, J Bater
Cons - S Connor (2), M Jones
Pens - S Connor (4)