Alex, who has been out with a knee injury since March, had hoped to be back playing in time for the Rugby World Cup, but was omitted from Vern Cotter’s squad of 31 which was announced last week.
An injury to another player could still see the head coach call on Alex but the Scotland head coach said the Warriors back would have to play a PRO12 game first.
Speaking in today's Evening Times, Alex said: “I came back, did a little running, but I had a bit of swelling on the joint so I’ve had to ease back slightly, which is frustrating. It’s still going well.
“It’s obviously disappointing not to be involved [in the World Cup], but it’s one of those things. It wasn’t quite right, so I couldn’t be involved. I’ve just got to focus on getting back fit with Glasgow and just playing when it’s right.
“Obviously I knew it was going to be a push to get back fit. It’s just frustrating that I came so close and was just not quite right, but I’d rather take an extra couple of weeks than go out there undercooked.”
Asked if there was a chance of taking part this weekend, Alex said: “No, sadly not. We’re just assessing it week on week - push it and see how it goes.
“I’m just back at Glasgow and focusing on getting back fit and getting back playing - and hopefully enjoying it. It’s just a battle to try and keep the swelling down. You can’t progress if there’s swelling.”