Neil Lennon was missing several players – including Odsonne Edouard and Ryan Christie – and drafted in young defender Steven Welsh and debutant Diego Laxalt.
But Ross, capped 13 times for Scotland, said the team-line was an Old Firm boost to Rangers who went on to win the match 2-0 and move four points clear at the top of the SPFL Premiership.
He said: “As soon as I saw the team-lines the writing was on the wall for Celtic. They have a good squad but that starting XI is probably the weakest I’ve seen in the last 20 years.”
Discussing the title race on BBC Sportsound he added: “This will go to the wire. I think the gap has closed because Celtic have regressed rather than Rangers having a massive progression.”