The injury ruled Alex out of Scotland's summer tour but the big centre was in Glasgow's starting line-up for last Saturday's pre-season friendly match with London Scottish.
Talking in today's Scotsman, Alex said: "It was great to get the run-out against Scottish.
“I had torn my hip flexor after 55 minutes of the PRO12 final at a ruck and I knew straight away it was a bad one.
“As it turned out, I missed the Scotland summer tour and it’s taken me 12 weeks to rehab the injury with some very intense physio, but I got the start against the Exiles and came through with no reaction, trained again yesterday and I’m fine. So I’m good for Saturday and I’ll just have to wait and see if I’m selected.
“We have tremendous strength in depth at centre and right across the backs. Obviously James Downey has come in from Munster to add to that competition and he has huge experience at the top level in European rugby which will benefit us.
“In training, the way the boys have slotted in and out of the combinations and the variety, in terms of the strengths each one of us have, really complements well.
“When the competition is so strong it can only benefit a team and it means that no one has the comfort zone of a guaranteed start.”
Leinster May have entered the early stages of the post-Brian O'Driscoll era but the Glasgow centre says the Irishmen won't lack for leadership on Saturday at Scotstoun.
He said: “Leinster may have lost Brian O’Driscoll and Leo Cullen to retirement but I don’t see that as an issue for them.
“They have leaders all across the park and established internationals like Gordon D’arcy and Zane Kirchner, to name but two.
“So I think that whatever XV they put out, it will be packed full of internationals as usual and full of quality and we will have to be at our best to beat them.
“Obviously we have lost to Leinster in two play-off semis and then the final last season and that hurts but we have to use that as a motivation.
“If we want to beat them then we must make sure that we do the basics to the best of our ability and make sure that there are no periods when we switch off. That happened in the final and it cost us dear. On Saturday, we need to stay completely focussed for the full 80 minutes.
"The last time we were at home was the play-off semi-final with Munster and it was a sell-out of 10,000 and the fans really gave us a lift. So, hopefully, this Saturday will be along the same lines.
“But we had great support for the whole of the campaign the last time around and it gives us a lift when we are arriving at Scotstoun and already there are fans in the car park milling around and wishing you ‘all the best’.
“If we can get the same level of backing we got for that semi with Munster this weekend then it can make a difference to us.”
Glasgow's assistant head coach Shade Munro says Alex’s return to full fitness has come at just the right time.
He said: “It is a massive plus to have Alex back at this stage and he is definitely ahead of schedule.
“Initially, Alex was not expected to be back for the beginning of the season.
“Alex has played a lot of rugby and the way he has recovered from the hip flexor injury means that he will have had a bit of a rest in terms of playing on summer tours.
“He was maybe a bit rusty early on against Scottish but, as the game went on, he got better and better and he finished it as one of our best performers.
“So it’s a big plus to have him back, fit and available for the start of the campaign.”