WASHINGTON -- With two days left before the non-waiver Trade Deadline, Nationals general manager Mike Rizzo is trying hard to improve a team that is currently in fifth place in the National League East and on a five-game losing streak.

Earlier this week, Rizzo improved Washington's bench by acquiring outfielder Jonny Gomes from the Reds in exchange for outfielder Bill Rhinehart and left-hander Chris Manno.

Rizzo also wants to acquire a center fielder. B.J. Upton of the Rays and Denard Span of the Twins have been mentioned the most in trade talks.

Span is currently on a rehab assignment after suffering a concussion in a home-plate collision in early June. Before the injury, Span was hitting .294 with a .361 on-base percentage in 56 games for the Twins, who are looking for a reliever.

If the Nats were to acquire Span, he would be Washington's leadoff hitter. The club has tried Danny Espinosa, Ian Desmond, Jerry Hairston Jr., Roger Bernadina and Rick Ankiel at the leadoff spot, and none have worked out. They entered Friday's action against the Mets hitting a combined .194 with a .265 on-base percentage.

Trade Include

Of all the center fielders the Nationals are looking at, Upton is the one Rizzo really wants, according to a baseball source. The Nationals believe a change of scenery will help Upton. He would be close to home, which is in Virginia, play with his childhood friend, third baseman Ryan Zimmerman, and be in the middle of the batting order.

The Nationals are also trying to trade right-hander Jason Marquis. He is a free agent after this year and the Nats most likely will not get compensation for him if he walks. A baseball source told MLB.com Thursday night that the Tigers have interest in Marquis. It's not known who Washington wants in return, but it would not come as a surprise if it wants a young player who can help the club long term.

Marquis said he would like to stay with the Nationals and would like to get a multiyear deal. But with Chien-Ming Wang, Stephen Strasburg and Brad Peacock on the way, one has to think Marquis will be one of the first to be dealt before the Deadline.

"We think we are going to be active, we are going to be busy," Rizzo said. "If it's a prudent deal, then we'll make that deal. Like I said, we are looking to be buyers and sellers. If it fits us long term, we'll be all ears and interested."