The Red Sox and Tigers are believed to be the teams most focused on John Lannan, with a growing expectation that the Nationals left-hander will be dealt by the end of the spring.

Lannan was a 10-game winner and had a 3.70 ERA in 33 starts for Washington last season, but the Nationals rotation became much more crowded when the team first traded for Gio Gonzalez and then signed Edwin Jackson as a free agent. With Stephen Strasburg, Jordan Zimmermann and Chien-Ming Wang also expected to have spots in the opening day rotation, there's no room for Lannan or Ross Detwiler.

The Nationals need to keep some starting depth, because they plan to limit Strasburg's innings and can't be sure how much they can rely on Wang. But sources say they are motivated to move Lannan, who will make $5 million this year.

Lannan's contract is big enough that it could scare off some potential trade partners, such as the Mets and Padres. The Astros have also had some interest in Lannan, sources say.

The Red Sox and Tigers both came to spring training with holes in their rotation. For now, the Red Sox have Daniel Bard and Alfredo Aceves in the final two spots, while the Tigers are looking at a group of young starters, including lefty Andy Oliver.

The Tigers have had their scouts watching all available and potentially available starters this spring, and one source suggested that they have yet to have any detailed talks with the Nationals about Lannan.

The Nationals are still looking for a long-term answer in center field, but they don't necessarily need to find it in a Lannan trade. The outfielder who is believed to interest them the most this spring seems to be Arizona's Gerardo Parra, and any deal for him is unlikely to include Lannan.

Diamondbacks general manager Kevin Towers told reporters Tuesday that he hasn't had any trade talks involving Parra this spring.

The Nationals explored many center field options over the winter, including Peter Bourjos of the Angels, Adam Jones of the Orioles and B.J. Upton of the Rays. It doesn't appear that any of those are a real possibility at this point, however.

For now, the Nationals have Roger Bernardina in center field, but if and when Bryce Harper makes the team in right field, Jayson Werth would likely slide over to play center field. The Nationals still want to find a long-term answer there, however, because the plan for next year has Werth in left field with Michael Morse moving to first base (Adam LaRoche is only signed through 2012).