An ‘A’ for off-season effort.

An ‘A for improvement.

And an ‘A’ in terms of being able to handle what could be an increased role during the coming season.

Manning, the Colts’ 10-year veteran quarterback and a seven-time Pro Bowl selection, said on Wednesday afternoon he believed Addai – the only NFL rookie to rush for more than 1,000 yards last season – was very much ready to be the team’s feature running back.

And if that means carrying the load for much of the season, Manning said he’s ready for that, too.

“I think Joseph has challenged himself on that,” Manning said Wednesday as the Colts (0-2 in the preseason) prepared to play the Detroit Lions (2-0) in a preseason game at the RCA Dome on Saturday at 7 p.m.

Edgerrin James, a four-time Pro Bowl selection, was the Colts’ feature back from 1999-2005, and in nearly every season, he received the majority of the carries.

Last season, with James having signed as a free agent with the Arizona Cardinals, veteran Dominic Rhodes and Addai shared carries, with Rhodes starting all 16 regular-season games and Addai starting in the playoffs.

Rhodes signed with the Oakland Raiders as a free agent this past off-season, and Manning said Addai appears ready for the larger workload.

“Edgerrin, for a lack of a better term, was a freak of nature from that standpoint,” Manning said. “I remember asking him, ‘Are you all right? Are you tired?’ Edgerrin could handle that. I think Joe wants that responsibility. He trained hard this off-season.

“We’re going to let him accept that challenge.”

The Colts’ backup running back position has been an off-season focus, and Colts Head Coach Tony Dungy said Wednesday it remains a priority, with second-year veteran DeDe Dorsey, Canadian Football League veteran Kenton Keith and undrafted rookie Clifton Dawson competing for the role.

Dungy said one of those players could get work with the first team Saturday, a game in which the starters are expected to play into the third quarter.

Manning said Wednesday while depth “is crucial in the NFL, I don’t think you say, ‘two backs’ as much as you say, ‘Who are the backs?’”

“I think when you have a guy like Joseph on the field as your starting back, you have to ask yourselves, ‘Are we as good with him off the field as not off the field?’’’ Manning said.

Rhodes last season rushed for 641 yards and five touchdowns during the regular season, with Addai leading all NFL rookies with 1,081 yards and seven touchdowns.

In the postseason, Rhodes rushed for 306 yards and a touchdown and Addai finished the playoffs with 294 yards and two touchdowns rushing.

“Last year, you could say, ‘Dominic and Joe, you feel good about both of them being in on a 3rd-and-1 and a two-minute drill and a red-zone drill,’ because Dominic was proven and Joseph proved in a short amount of time he could handle it,’’ Manning said. “At this point now, you’re going to have the same situation with the younger backs and I think until that comes about, you’ll have Joseph in there. I think he deserves the opportunity to kind of carry that load.

“In the course of the season, you’re always going to need the young back to step in, and make a critical block and make a critical 3rd-and-1. We’ve got the young guys working hard, battling, but I’ve been proud of Joseph and how he’s worked this off-season to try to get his body ready to carry a 16-game load.”

Also on Wednesday, Manning said while the offense has played just four series this preseason, he said he feels good about the progress the unit has made.

The first-team offense produced a first down on all three series it played against Chicago on Monday, driving for a 4-yard touchdown run by Addai on its final series.

“It’s hard if it’s three three-and-out series,” Manning said. “The other night, we had some first downs on each drive. Even though we only scored seven, we had multiple plays on the drive. You kind of felt like you were in a little flow. When he (Dungy) took us out, we kind of felt like it was the right time. We had just scored. We kind of felt like, ‘Hey, we could really continue to execute at this point.

“That’s kind of what you want to ask yourself, ‘Do you feel comfortable?’ It was a good way to finish that game and hopefully, we can kind of pick that up with some good execution on offense Saturday.”

Entering training camp at the Rose-Hulman Institute of Technology in Terre Haute three and a half weeks ago, Manning – the NFL’s Most Valuable Player in 2004 and 2005 and the Super Bowl XLI MVP this past February – said one of his goals was to work extensively with rookies, including first-round wide receiver Anthony Gonzalez.

That’s still a focus in the final two weeks of preseason, Manning said.

“The main thing I’ve tried to concentrate on is getting as comfortable as I can with some of these new players,” Manning said, like Gonzalez or like the young receivers. (Veteran wide receiver) Aaron Moorehead is playing more.

“Those guys affect my job, so I want to be as comfortable with them as I can, go out there and hopefully do my job to the highest level as I can.”

Manning on Wednesday also said he expects the offense to be slightly more diverse this season. Late last season, with slot receiver Brandon Stokley injured, he said the Colts played two-tight end sets extensively.

With Gonzalez in the slot this season, Manning said “we’re working hard to get as comfortable and as confident in our three-receiver sets.

“The football is only so big,” Manning said. “You’d love to be able to drop back and have all five eligible receivers catch a pass on every play. Believe me, that would make things a lot easier on the field and in the locker room.

“Having that option is what we’d like to get back to. Last year, we were kind of forced into only being one-dimensional, two-tight end offense. We went out and said, ‘We’re going to play this formation first, second and third own. You’d like to be able to put your three wide-receiver set or four wide-receiver set out there and it may be a faster offense with that mix.

“To get back to that would be a nice option to bring back.”