Asymco's Horace Dediu predicts that the handset could move an initial 6 million units, 2 million more than the current iPhone 4S managed.
The iPhone 4S moved 4 million units in three days when it launched last year, while the iPhone 4 sold 1.7 million, and the iPhone 3GS around 1 million.
Dediu believes that Apple's newly announced smartphone is likely to draw in more upgrading customers than first time buyers.
He said: "There might be first time buyers, but the dedication required to ensure being first to have it usually means buyers are keen on the brand and are repeat customers."
The sales estimate is partially based on the iPhone 5's wider consumer base, with the device available in nine countries at launch, compared to its predecessor's seven.
"The performance of the [iPhone] 5 in the first weekend should be better on a volume basis simply because there are more existing customers who wish to upgrade and because there are more initial and significant launch countries," Dediu added.
The analyst also tipped the handset to hit the 10 million sales mark by the end of its first month.
Apple unveiled the iPhone 5 alongside new additions to its iPod Nano and iPod Touch lines at a press conference in San Francisco yesterday (September 12).
Photo gallery - Apple's iPhone 5: