Who pitches against Mets? (Strasburg placed on DL)

MILWAUKEE - When the Nationals scratched right-hander Stephen Strasburg from today's start with a recurrence of his upper back strain and decided to start righty Tanner Roark instead, it threw their rotation for this week's key home series against the Mets into disarray.

Instead of starting Roark, then right-handers Joe Ross and Max Scherzer against their division rivals, the Nats are now reassessing their options. They haven't yet announced starters for the series, which begins Monday night at Nationals Park.

And you thought the seven-game losing streak was the only thing causing consternation in NatsTown.

Ross is still the most likely to pitch Monday night against the Mets' Noah Syndergaard, but who will follow him in the rotation remains unclear. The Mets will pitch Matt Harvey on Tuesday and Stephen Matz on Wednesday.

Scherzer last pitched Friday night, so it's unlikely the Nationals will call on him with three days' rest. He'll likely be slotted for the series finale on Wednesday.

Tuesday? It's anyone's guess now.

If he isn't needed today or tomorrow, righty Yusmeiro Petit could make his second spot start of the season. He filled in for Strasburg on Monday night in Los Angeles, battling Dodgers ace Clayton Kershaw. But that would require both Roark and Ross to go deep in their starts. If they don't, the Nats don't have a long man besides Petit.

Right-hander A.J. Cole is scheduled to start today for Triple-A Syracuse. He's 5-4 with a 4.64 ERA in 14 starts this season and hasn't appeared in the majors since a 4 1/3-inning relief outing last May 23. Cole made his major league debut last April 28 in a spot start in Atlanta, allowing nine runs (four earned) in two innings in a game the Nats rallied to win 13-12 on a Dan Uggla homer.

If Cole pitches today, he's out of the picture for Tuesday. If he's scratched, he probably gets the call.

Cole is on the Nats' 40-man roster, but clearing a 40-man spot for a player not currently on it won't be a problem. The Nationals could move righty Taylor Jordan, who is currently recovering from May 28 Tommy John surgery, to the 60-day DL to open a spot.

Which brings up to two top pitching prospects, right-handers Lucas Giolito and Reynaldo Lopez, who are both at Double-A Harrisburg and not on the 40-man roster.

Giolito, 21, is 5-3 with a 3.17 ERA in 14 starts for the Senators, and last pitched June 21, when he allowed seven runs (five earned) in 4 2/3 innings at Portland. Giolito struggled early this season at Harrisburg, but went 5-0 over seven starts between May 9 and June 10. The Nationals are carefully monitoring his innings this season. He's currently at 71 innings, and the Nats won't go more than 15-20 innings over the 117 he pitched last season between Single-A Potomac and Harrisburg.

Lopez, 22, last pitched last night, which takes him out of the equation. He pitched eight shutout innings on seven hits at New Hampshire, improving to 3-5 with a 3.18 ERA in 14 starts.

Asking a top prospect like Giolito to make his major league debut against the defending National League champs would be asking a lot. But need may outweigh formality or desired preferences for the Nats in this case.

Two other options at Triple-A would be right-handers Taylor Hill and Austin Voth. Hill, 27, would be on normal rest, having last pitched June 22 at Pawtucket, getting a no-decision despite seven innings during which he allowed two runs on five hits. Hill is 3-6 with a 4.76 ERA in 14 starts this season for Syracuse. He's pitched in the majors before, going 0-1 with a 6.00 ERA in nine games, including a 2014 start. Voth, 24, is 4-3 with a 2.99 ERA in 14 starts with the Chiefs this season, and last pitched June 23 at Pawtucket, working six innings and picking up a win by allowing a run on five hits. He's never pitched in the majors.

Neither Hill nor Voth are on the 40-man roster.

Update: The Nationals have placed Strasburg on the 15-day disabled list with an upper back strain, and will announce a corresponding roster move tomorrow.