The 49ers legend made the comments to the Contra Costa Times and San Francisco Chronicle while promoting April's TPC Stonebrae Championship golf tournament.
"I think you go for it," Rice said. "A guy of that talent, you've got everything in place. You've got a defense that smacks you in the mouth. You just need a little more out of the offense. That's not knocking what Alex (Smith) did. (Manning) can take you to a whole different level."
NFL free agency begins March 13. Manning missed the 2011 season after undergoing neck surgery. He has four years left on his contract and reports out of Indianapolis is that the Colts and their longtime signalcaller will part ways at a Wednesday news conference.
"If they're going to invest that much money in Alex and they feel he can get the job done, then do it," Rice added. "I know he made significant improvement this year and did what was asked of him. If he can get more weapons around him and knowing he has a coach that has confidence in him, that he doesn't have to look over his shoulder, it might bring the best out of him."
Rice also shared his opinion on 49ers wide receiver Michael Crabtree, who has yet to meet the high standards that accompany his status as a first-round draft pick.
I just did not see separation (from defensive backs), Rice told the newspapers. I dont know exactly what he weighs. Maybe he needs to lose 10 or 15 pounds and be more explosive.