ST. LOUIS -- Stephen Strasburg won't make his next scheduled start for the Washington Nationals on Friday.

Strasburg was limited to four innings with upper-back tightness his last outing. The right-hander is scheduled to throw an extended bullpen session Thursday and manager Matt Williams said Strasburg would need at least two days after that before pitching.

Williams said it was possible that Strasburg, 8-6 with a 4.35 ERA, could be inserted into the rotation before his next turn but reserved judgment until after the session.

Tanner Roark will be recalled from the minors to replace Strasburg against Atlanta. Roark's start was abbreviated to two innings at Double-A Harrisburg on Monday so he would be available.