The Washington Nationals have two everyday players who are hitting better than .300, two everyday players who have driven in 40 runs, two everyday players who have remained healthy, and in the lineup, virtually all season. And both of them -- first baseman Nick Johnson and right fielder Jose Guillen -- may miss all or part of a three-game series against the Pittsburgh Pirates that begins today.

Johnson, the Nationals' cleanup hitter, came down awkwardly on his right heel Sunday while scoring in a loss to the Toronto Blue Jays, and while X-rays and an MRI exam on Sunday -- and a subsequent MRI yesterday -- revealed no fracture, he will likely be out between three and seven days, meaning he may miss a weekend series in Chicago against the Cubs.

Guillen, who hits third, played the entire series against the Blue Jays, but came up with an extremely sore right shoulder which, according to Nationals General Manager Jim Bowden, Guillen believes he hurt in a collision at the plate. Guillen had an MRI exam yesterday as well, and he will be evaluated on a daily basis.

"Injuries happen to everyone," Bowden said last night. "We'll just have to overcome them. But these are two guys that are obviously extremely important to this team."

Johnson is hitting .320 with eight homers and a team-leading 42 RBI, and his on-base percentage of .444 is the second-best in baseball. Losing him at a time when the Nationals finish a homestand against the sub-.500 Pirates and then take on the Cubs is less than desirable, particularly when Washington, which leads the National League East, is already without second baseman Jose Vidro, who has been on the disabled list since early May with an ankle injury.

Team physician Bruce Thomas said yesterday that it is hard to predict exactly how long Johnson's injury, diagnosed as a deep bone bruise, will keep him out. Bowden, though, said Johnson felt "much worse" yesterday than he did Sunday, when he left the park limping.

"He said it was bothering him a lot more," Bowden said.

Bowden said the team, for now, isn't considering putting Johnson on the disabled list, "But you never know," he added. A trip to the disabled list would be Johnson's sixth in six years. His health, more than anything, has been the refreshing element in this breakout season.

Johnson has reached base by hit, walk or hit-by-pitch in 69 of the 74 games he has played. Veteran Wil Cordero and outfielder Brad Wilkerson, who normally starts in center, have plenty of experience playing first base. But for Wilkerson to move into the infield, outfielder Ryan Church -- who injured his left shoulder while slamming into the wall in Pittsburgh last week -- would likely have to be ready to play again. Church missed the weekend series against the Blue Jays, but was feeling better by Sunday.

"I think he'll be okay," Thomas said. "He got a lot better by the end of the weekend, and I think the rest helped."

Should he be ready to play, Church -- who is hitting .325, slugging .544 and has 28 RBI in 160 at-bats -- could play alongside Marlon Byrd, with whom he normally platoons in left field. Robinson considers Wilkerson a capable first baseman, and he started 78 games at first base last season, when Johnson missed time with back problems and a fractured cheekbone. Wilkerson has just one start at first this year.

Cordero would be the other option, and if he starts in Johnson's place, it could be his final opportunity to prove he should stay with the Nationals. He is hitting .038 this season, with just one single in 26 at-bats. When the team played interleague games in Anaheim and Texas, he was given the chance to get four at-bats a game as the designated hitter, a move Manager Frank Robinson thought might serve as a spark. It didn't, and Cordero risks losing his roster spot when Vidro returns. The team could place Cordero, who already has had surgery to repair a torn meniscus in his left knee, back on the disabled list at that time.

Guillen also fouled a ball off his leg on Sunday, an injury for which he declined treatment, Thomas said. Guillen hates being out of the lineup, and he and Johnson are two of the team's three leaders in games played, with 71 and 74, respectively. (Shortstop Cristian Guzman has played in 73).

Yet even with Johnson and Guillen, only one team, Houston, has scored fewer runs than Washington. And tonight, the Nationals could very well try to maintain their lead in the division without two of their best hitters.

Nick Johnson likely will be sidelined between three and seven days with a deep bone bruise in his heel. Nick Johnson, injuring his right heel on this play, felt "much worse" yesterday than he did on Sunday, when he left the ballpark hobbling, said Nats GM Jim Bowden.