Addai was one of three Colts players catching passes last week from the four-time league MVP. On Wednesday, he told The Associated Press that Manning is putting some zip on his short passes.
"He's not throwing deep-level passes, but the short stuff is really good enough to play," Addai said.
The comments come three days after team vice chairman Bill Polian ruled Manning out of the Colts' final two games and one day after coach Jim Caldwell said Manning would not participate in any of the remaining full-team workouts before Indy's season finale Jan. 1. He is expected to continue throwing before or after practice.
Both have said that Manning is progressing well from Sept. 8 neck surgery, though he has not played in a game or practiced full bore since undergoing his third surgery in 19 months.
Last Wednesday, Manning put on a helmet and pads and did a post-practice workout that included taking snaps from center Jeff Saturday and throwing with Addai, receiver Anthony Gonzalez and a receiver from the practice squad.
On Tuesday, Polian said Manning's throws looked good and when asked whether he had decent velocity on the throws from 20 to 25 yards, Polian said, "That's correct."
Addai is one of the few people who can confirm that assessment.
"He's coming along good," Addai said. "He's looking good and he throws a good ball."
With Manning, the Colts were a perennial Super Bowl contender.
Without him, the Colts (1-13) have barely been able to avoid the dubious distinction of becoming the second team in NFL history to go 0-16. On Sunday, the Colts beat Tennessee 27-13 for their first win since 1997 with a quarterback other than Manning.
Indianapolis plays its home finale Thursday night against AFC South champion Houston (10-4), then closes the season at Jacksonville on Jan. 1. Polian has already said Manning will fail the team's postseason physical, which will make him eligible to continue throwing at the team complex during an uncertain offseason.
The Colts still must decide whether to pay Manning a $28 million bonus in March, let him become a free agent or possibly redo the contract to make it more salary-cap friendly.
It's also likely Indianapolis will have the No. 1 overall draft pick, a slot that most expect to be used on Stanford quarterback Andrew Luck. That would give them the opportunity to keep Manning, if healthy, with Luck expected to become Manning's eventual successor.
And Polian believes the team will have all the information needed to make the right decisions.
"We have always felt that we would have a good sense of where we are, because we have always known that this is what the procedure would be," he said Tuesday.