Stephen Strasburg takes the field before a baseball game against the Philadelphia Phillies at Nationals Park on May 23. (Andrew Harnik/Associated Press)

After an off day Monday, the Nationals will return Tuesday looking to extend a stretch of historically good pitching. Who exactly will be on the mound when the Braves come to town, though, is still a bit of a mystery.

Stephen Strasburg could return from his 15-day disabled-list stint — he gave up one earned run in a rehab start last Wednesday and sailed through a bullpen session Saturday with no announced setbacks. After that bullpen work, Washington manager Matt Williams said he would not pencil Strasburg back into the rotation until after the team could evaluate how Strasburg felt Sunday. And after Sunday’s 9-2 win, Williams said the team was going to look at him on Monday. Then he said a decision might not come until Tuesday morning.

If it’s not Strasburg on the mound, Tanner Roark would likely be the man tasked Tuesday with extending what was the best three-game stretch of defense of the season for Washington, as it gave up just three runs over the course of a three-game sweep of Pittsburgh.

Without a firm announcement from Williams, here are some clues about Strasburg’s return: Last week, Strasburg said he was feeling as good as he felt since spraining his ankle during spring training. Sunday, Bryce Harper, well accustomed to injury-related speculation himself, said “We’ve got one of the best staffs in baseball with Stras coming back this week against the Braves.” Minutes later, Gio Gonzalez mentioned that Strasburg was back in the rotation while listing reasons for optimism, for whatever that’s worth.

When he does return, Strasburg will look to improve his 6.55 ERA and 1.72 WHIP, both of which are the lowest among active Nationals. They also represent career lows for the 2009 No. 1 overall pick.

Strasburg has generally struggled against the Braves. His 4.24 ERA against the team is the highest against any opponent he has faced at least five times. According to the team, Jordan Zimmermann will pitch Wednesday and Doug Fister Thursday, which means Roark would be skipped. Williams has not said what will happen to Roark when all five starters are healthy, though it is likely he will head back to the bullpen, where he began this season.

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