Wafer, a 6-foot-5 shooting guard, will leave for Greece on Friday, said Giovanni Funiciello, who is Wager's international agent.
The contract will allow Wafer to opt out after one season, but only to sign with an NBA team. Wafer confirmed the deal Wednesday after it was reported by KRIV-TV in Houston.
Wafer, 24, averaged 9.7 points and shot 39 percent from 3-point range for the Rockets in 2008-09. He made about $800,000 in his only season in Houston.
Funiciello said the offer from the Greek team was the best one Wafer got over the summer.
"Financially, he wasn't going to get that type of an offer in the NBA," Funiciello said. "As far as I knew, he really didn't have anything concrete as far as the NBA was concerned."
The Greek club team also recently signed former Denver forward Kleiza.
Denver Nuggets officials said this week that Kleiza has agreed to a two-year deal with Olympiakos worth more than $12 million.
The Rockets have spent the offseason shoring up their roster. On Wednesday, they addressed the loss of Yao Ming by signing center David Andersen to a multiyear contract.
The Rockets acquired the rights to the 6-foot-11 Andersen in a trade with Atlanta on July 14. Houston scrambled to find a center after announcing in June that Yao was out indefinitely with a hairline fracture in his left foot.
Information from The Associated Press was used in this report.