WASHINGTON -- The Nationals placed first baseman Adam Dunn on waivers Tuesday, according to a source outside the organization.

The move comes four days after the Nats unsuccessfully tried to deal Dunn before the non-waiver Trade Deadline. General manager Mike Rizzo said for weeks that he wanted a lot in return for the slugger.

That will still be the case now that Dunn is on waivers, which doesn't mean that he will leave the team. In fact, a lot of players are put on waivers and then pulled off.

A player exposed to waivers can be claimed by any team, and if there are multiple claims, the player would be offered to the team with the worst record. At that point, a team has 48 hours to either try to work out a trade with the claiming club or remove the player from waivers.

A player can only be pulled back from waivers once, but if he clears waivers either the first or second time through, a team can attempt to trade him to any club. Most players go through waivers, so it is a common practice.

"There is always a possibility [we could make a trade before that date]," Rizzo said recently about the Aug. 31 deadline. "We are always looking to do our jobs and improve the ballclub. When contenders are interested in your players, it means you have playoff-caliber players on your team that people want."

Dunn said he didn't have any idea about being placed on waivers.

"I don't even know what that means," Dunn admitted.

The big unknown is if Dunn will sign an extension before Aug. 31. Dunn hopes so, but his price may be too high. He is asking for a four-year deal, but is said to be willing to listen to a three-year offer.

"Yeah, there's a possibility, but I don't know what the percentage is. It's out of my control. I'm not worried about it," Dunn said. "You cannot not think about it, because every day it's everywhere, and people are asking you about it every second of the day. I'm glad the [non-waiver] part of it is over. I guess I have to deal with this now."

Dunn had to deal with the waiver deadline two years ago. On Aug 14, 2008, the Reds traded Dunn to the D-backs for catcher Wilkin Castillo and a player to be named, which turned out to be right-hander Micah Owings.

Dunn then became a free agent after the season and signed a two-year, $20 million contract with the Nationals.

In his first year in Washington, Dunn hit a career-high .267 with 38 home runs and 105 RBIs. Entering Tuesday's action against the D-backs, Dunn was hitting .276 with 26 home runs and 67 RBIs this season.