That will leave Roger Bernadina starting in right field and Tyler Moore starting in left.
Bernadina is hitting .129 on the season. Moore is batting .163.
Ryan Zimmerman will move back up to his familiar No. 3 spot in the order with Harper out, Adam LaRoche will hit cleanup and Ian Desmond will bat fifth.
Davey Johnson will have a three-man bench tonight, consisting of Chad Tracy, Steve Lombardozzi and Wilson Ramos.
Old buddy Edwin Jackson is back at Nationals Park today, this time as a member of the Cubs.
Jackson, who won 10 games with the Nats last season, signed a four-year, $52 million contract with the Cubs this winter. The veteran right-hander has gotten off to a rough start to this season, going 0-5 with a 6.39 ERA in his first seven starts.
He'll get a chance to face his former team tomorrow, as he'll oppose Stephen Strasburg in the second game of this three-game set.
Jackson was out on the field earlier, sharing hugs and handshakes with his old teammates and coaches. He played just one season here in the district, but was a popular player in the Nats' clubhouse.
Another former National returns to D.C. today - Alfonso Soriano.
It might seem like forever ago that Soriano signed that eight-year, $136 million deal with the Cubs, but remarkably, he still has one year left on that deal after this season. He's making $18 million this year and will make the same in 2014 in the final year of that deal.
Tonight, the Nats will square off against Cubs ace Jeff Samardzija, who is 1-4 with a 3.09 ERA thus far this season.
Samardzija is 10th in the majors with 52 strikeouts, and he has a solid 1.168 WHIP.
Ross Detwiler tries to get back in the win column tonight after getting stuck with the loss in his last three outings. The left-hander is 1-3 with a 2.50 ERA this season.
For the Nats
CF Denard Span
RF Roger Bernadina
3B Ryan Zimmerman
1B Adam LaRoche
SS Ian Desmond
2B Danny Espinosa
LF Tyler Moore
C Kurt Suzuki
LHP Ross Detwiler
For the Cubs
SS Starlin Castro
3B Cody Ransom
1B Anthony Rizzo
LF Alfonso Soriano
RF Scott Hairston
C Wellington Castillo
CF Ryan Sweeney
2B Darwin Barney
RHP Jeff Samardzija