VIERA, Fla. (AP) - Bryce Harper woke up with tightness in his left calf so, after he failed to get it loose, the Nationals scratched their top prospect from Thursday's game against Houston. Astros starter Livan Hernandez left under much scarier terms.

Hernandez was hit in the lower right leg by a drive off Ryan Zimmerman's bat in the bottom of the third inning of Washington's 8-0 win over the Houston Astros.

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In the end, neither injury was considered serious.

``I've never felt it before,' Harper said of his calf injury. ``That was the weird thing. I felt it this morning and I was just like, `I have no clue what's going on right here.' So I came in, tried to ride the bike, tried to loosen it up. I didn't feel it when I swung at all.'

The 19-year-old did, however, feel it while moving around in the outfield, so the Nationals decided to be cautious. Harper said he hoped to get back as early as Friday or Saturday, but manager Davey Johnson said the No. 1 overall pick in the 2010 draft would likely be held out for at least two days.

``I'm sure he'll be bugging me,' Johnson said when told about Harper's timeline. ``But it's a long spring. No hurry.'

Harper had played in four of the Nationals first five games and was hitting .455 this spring in his bid to win the starting right field job coming out of camp. He reiterated that he didn't expect his injury to be anything long term.

``Absolutely not,' he said. ``It's spring training. I'm trying to be as careful as I can. I'd rather miss two days, three days down here than five (days) during the season.'

Hernandez was optimistic.

``I feel good now,' Hernandez said. ``Let's see (how it is) tomorrow. There's no bruise. It's not puffy, so it will be all right. I think I had one more hitter, so it's better to get out of there.'

The 15-year veteran right-hander gave up two runs on three hits and struck out two in 2 1-3 innings. One of those runs came on Zimmerman's homer to right field in the first inning.

Zimmerman, who had two hits and two RBIs, led off the third inning and lined a changeup up the middle. The ball hit Hernandez in his lower right leg, but he recovered in time to throw Zimmerman out at first base. He was then replaced by Lucas Harrell.

Hernandez, a non-roster invitee, was more interested in how his arm felt after Thursday's outing.

``The more important thing is I feel better than the first time (I pitched this spring),' he said. ``The breaking ball was better, the changeup was breaking very good and the sinker was working very good, too. I feel good today. It's a good sign.'

Nationals starter Edwin Jackson had plenty to feel good about, too. He threw four scoreless innings, giving up two hits and striking out three.

Johnson called Jackson's performance ``superb.'

The Nationals have been trying to get the right-hander to not think about his mechanics and just throw the way he feels most comfortable. Jackson certainly looked at ease Thursday. He just wasn't sure how he got there.

``Who knows,' Jackson said. ``When you're going good, you don't really know what it is. Something just clicked and whatever mechanics I had, I was able to just continue to repeat them and throw pitches across the plate.'

Eury Perez, who started in place of Harper, had two hits and an RBI. Mark Teahen drove in two runs. Four Nationals pitchers combined to hold Houston to three hits.

NOTES: Nationals first baseman Adam LaRoche and outfielder Michael Morse both got some at_bats in a minor league game Thursday. LaRoche (ankle) is expected to rejoin the lineup Saturday. Morse, who has been bothered by a strained lat muscle, was feeling better Thursday. Johnson said Morse feels fine batting, but is still having difficulty throwing the ball. Johnson didn't think the injury was serious . The Nationals first cuts of the spring will likely take place Monday . Astros third baseman Jimmy Paredes, recovering from a sore left wrist, made his spring debut Thursday and struck out in his only at-bat. He is expected to start Friday against Toronto ... . Catcher Humberto Quintero was back in camp Thursday after being examined in Houston by Dr. David Litner and receiving an injection to treat what manager Brad Mills said was a bulging disc in his lower back. He was expected to play catch in Kissimmee Thursday and could catch a bullpen session on Saturday. He won't start swinging a bat until next week.