Strasburg's return creates a logjam in the team's rotation, so the Nationals are moving pitcher Doug Fister to the bullpen.
Williams announced that rookie Joe Ross, who was previously sent back to Triple A when Strasburg came off the DL in July, will remain in the rotation.
Fister has struggled of late this season and currently boasts a career-high 4.60 ERA and 1.419 WHIP through 15 starts.
In seven major-league starts, Ross has a 2.80 ERA and 47 strikeouts in 45 innings.
Strasburg was placed on the DL in early July with a left oblique strain. He recently completed a rehab stint at Triple A Syracuse.
- Molly Geary