However, the Glasgow man is optimistic of making a strong start to the season despite struggling to find full fitness.
"I came back doing a bit of running but I had a bit of swelling come back into it so I've had to ease back slightly which is frustrating," Dunbar told the Scotsman.
"But it's still going well. We're just going to have to wait and see.
"I'm just back at Glasgow now and focusing on getting back fit and playing and hopefully enjoying it.
"It was a little bit disappointing [to not make the squad] but obviously I knew it was going to be a push. It was just frustrating that I came so close and it just wasn't quite right.
"But I'd rather take an extra couple of weeks than go out there undercooked and do it again. It's getting there but I need to get the swelling in the joint down."
Dunbar will now look to cement his place in the Glasgow side with many of his team-mates on international duty for the early season games.
The Warriors, who won last season's GUINNESS PRO12 at the Kingspan Stadium in May, will be hoping to reach a final a little closer to home this time, as the 2016 edition comes to a head at Murrayfield.
"It will be good for Scottish rugby," added Dunbar. "You saw all the fans who went across to Ulster to the final last year, so hopefully we can get a Scottish side in the final, a big crowd and it's a great day."
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