However, the hard-hitting lock has revealed he has fully recovered now and is itching to get involved against Zurich Premiership giants Sale on Friday night.
Jason said: "It has been very frustrating to be on the sidelines, but I am 100% better now and have been training hard since New Year's Day. We have had some good, hard training sessions with Glasgow this week and I'm looking forward to having the opportunity to play against Sale either from the start or from the bench.
"I picked up concussion playing for Scotland in the final Scottish Mutual Autumn Test match against Fiji and then I hurt my back in training on Christmas Eve.
"There are a few reasons behind why it is taking me so long to get back playing. Because of my concussion I had to take things very easy when I returned to training. It is my first extended spell on the sidelines this season and it has been difficult to take, but I am over that now and am concentrating fully on this match."
If Glasgow can improve their try count and point differential then there is still a slim hope they can edge past Pool rivals Llanelli and Bourgoin and qualify for the knockout stages.
It is a tall order against a team currently placed second in the English Premiership thanks. Yet, White is adamant that Glasgow can pull off an upset. He predicted: "It is going to be a really tough game. We have not been firing on all cylinders recently. But we have got to simply roll our sleeves up and try and pick things up for this match. Props Lee Harrison and Cameron Blades should also be available for selection after injury.