Guillen, 29, batted .283 with 24 home runs and 76 RBIs in 148 games with the Nationals in 2005.
Washington exercised the option in the contract that Guillen signed with the Los Angeles Angels of Anaheim before the 2004 season to extend it through 2006. The Dominican will earn $4 million and then have the chance to become a free agent for second time in his career.
From the Nationals' training camp in Melbourne, Fla., Guillen told ESPNdeportes.com that he'd like to resolve any contractual issues during training in order to avoid distractions once the season has begun.
"After the action begins, no one wants to think about anything else," said Guillen.
To lead the negotiations with the Nationals during spring training, or with other clubs once November is over, Guillen re-signed Adam Katz and Andy Mota as his agents.
"Katz and Mota have managed almost my entire career, and I think that this is the best for me right now," said Guillen.
Guillen reported to the Nationals' training camp last week, before any of his teammates, in order to continue the rehabilitation of his left shoulder and to prepare for the first game of the season on April 3.
The surgery that Guillen had last November to repair a shoulder ligament has jeopardized his ability to play the first weeks of the season.
"Right now I feel strong and optimistic of not missing anything," said Guillen, who is batting .276 with 134 home runs and 534 RBIs over nine seasons with Pittsburgh, Tampa Bay, Cincinnati, Arizona, Oakland, Anaheim and Washington.
"I think I have a specific value on the market, and I think the Nationals know that. Up to now I'm satisfied with the treatment the organization has given me, especially GM Jim Bowden and manager Frank Robinson," said the player about his conversations with the Nationals.