Neil McCann feels Sunday's derby clash will be the true measure of how far Celtic have come in the early weeks of the season.
New manager Ange Postecoglou had a rocky start with no wins in his first three, but has turned that round with back-to-back 6-0 wins in the Premiership.
Fans have been blown away by the exciting and attacking football their side has been playing, and are in confident mood heading to Ibrox.
But while he's been impressed with Postecoglou's side in recent weeks, McCann feels it's the first derby of the season that will be the acid test of how much has changed.
He said on Sportscene: "This is a tester for Celtic.
"This is a barometer to see where Ange's team is.
"They're blowing teams away and are scoring freely, going up against a Rangers side who were sensational last season - but they've not started the way they finished last season.
"So these are two sides coming to collide and this will be an indication of where the season's going to go. I can't wait."
