Nationals right-hander Stephen Strasburg has been scratched from Friday's scheduled start for an unknown reason. Fellow righty Ross Ohlendorf will start in his place.

James Wagner of the Washington Post notes the 25-year-old Strasburg felt tightness in his hamstring 11 days ago but it's unclear if that's why he has been scratched. Strasburg spent a little more than two weeks on the DL with a lat strain earlier this season. He missed time with shoulder inflammation in 2010 before missing most of 2011 following Tommy John surgery.