Koundouris crashed the Supabarn Supermarkets-backed car at Siberia (Turn 6) and collided with the tyre wall during the second unofficial practice session.
The team will miss the rest of Friday’s practice and are hoping to have the car ready in time for Saturday’s back-to-back qualifying sessions.
If the team gets the car ready in time, Koundouris and his brother Theo could give it a shakedown in the 60-minute pre-qualifying on Saturday morning.
“The tyres weren’t quite on,” said Koundouris.
“The car felt good, but I pushed too soon. I touched the grass and spun around.
“I used just a little bit too much road and that’s the result.
“I didn’t hit the wall very hard. It is what it is, but the most disappointing thing is that Theo has missed out on practice and for the first time this year, the car felt really good.
“We felt like we had a really fast car. We’ve come a long way with the set-up.
“In the first practice session, we were on old tyres and our times were really good. So it’s disappointing that I’ve let the team down.
“But, tomorrow is another day.”
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Koundouris wasn’t the only car to have issues. Melbourne Performance Centre’s Will Brown suffered a tyre blow-out.
“Felt alright going down the straight,” Brown told Speedcafe.
“I was lucky actually, because I had rolled out it. Bit of body damage but all good, we roll on.”
The SRO-promoted GT Festival takes place across August 23-25.
Headlined by Fanatec GT World Challenge Australia powered by AWS, the GT3 series will be supported by Monochrome GT4 Australia Series and Australian Production Cars.
Spectators will have free entry across the entire weekend with coverage live on Foxtel and Kayo as well as the GT World YouTube channel.