The Official Online RBS 6 Nations Store is open. The store has everything you need to get behind your team during the RBS 6 Nations, plus the store is now fully stocked with a much wider range of rugby merchandise.
The 22-year-old will definitely miss Edinburgh's David Lloyd 1872 Cup return match against Glasgow at Firhill on Friday.
Edinburgh's head physiotherapist TJ Johansson said: "Ross underwent the operation today to ascertain the full extent of the damage to his knee.
"We will wait for the results before determining how long his rehabilitation programme will last."
Rennie, who earlier this month received a two-week ban for a tackle on Wasps' Paul Sackey in the European Cup, played in Scotland's match against Ireland in the 2008 RBS 6 Nations.
If fit he would provide competition for the No.7 jersey to the impressive John Barclay of Glasgow.
It is the second injury blow in as many days after winger Nikki Walker was almost certainly ruled out of the 2009 RBS 6 Nations with a hamstring injury.