The bank had originally forecast this year's growth at 8 percent, slowing from an estimated 8.3 percent expansion in 2011.
The International Monetary Fund (IMF), which has given a $2.6 billion loan program to Sri Lanka, earlier said the economic growth would be less than 7.5 percent.
"We are getting ready to lower our growth forecast, around next week's monetary policy announcement. It won't be below 7 percent," Central Bank Governor Ajith Nivard Cabraal said.
The bank meets on interest rates next Wednesday, when it should announce the changed forecast formally. Two other central bank officials confirmed the revision is under way.
"We will be looking at all the conditions. There are some areas going to be better and some areas not so good. So we are taking a calculated call," Cabraal said.
A record trade gap and a growing current account deficit forced the central bank to raise its policy rates for the first time since 2007.
The central bank last month halted its defence of the rupee at a specific price against the dollar, having spent more than $2.7 billion of its foreign exchange reserves last year to stave off depreciation.
That removed a point of friction with the IMF and relieved pressure on its fast-dwindling reserves.
Market interest rates have risen by 115-143 basis points since the bank raised its main policy rates by 50 basis points to 7.5 and 9.0 percent respectively on Feb. 3.
The rupee has also depreciated more than 5.7 percent since the central bank stopped defending it on Feb. 9.
The country is expected to have recorded a balance-of-payments deficit in 2011, although the official figures have not been released yet.
