HOUSTON -- As the Astros come to terms with the news they won’t have right-hander Justin Verlander if they reach the postseason after he announced Saturday that he's undergoing Tommy John surgery, the club will have to determine the makeup of its pitching rotation for the playoffs sans its ace.

The only sure thing at this point, barring injury, would be veteran Zack Greinke, who carried a shutout into the seventh inning of Game 7 of the World Series last year. The other two starters in the best-of-three Wild Card Series would come from the group of Lance McCullers Jr., Jose Urquidy, Framber Valdez and Cristian Javier, who threw four strong innings in Saturday’s 3-2 win over the D-backs at Minute Maid Park.

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“We’re talking about it some, but our main concern is trying to get there,” Houston manager Dusty Baker said. “Once we get there, then we’ll talk about it and try to go out there with the best people possible.”

The Astros (26-26) have a three-game lead over the Mariners for second place in the American League West, which brings a guaranteed berth in the expanded 16-team postseason. They inched closer to a playoff spot by rallying for a pair of runs in the sixth inning on an RBI double by Jose Altuve and a go-ahead RBI single by Kyle Tucker.

It was Houston’s fifth win in its past 16 games, and it now has a magic number of five to get into the postseason.

Here’s a closer look at the four pitchers who could potentially start along with Greinke in the postseason.

RHP Cristian Javier: 4-2, 3.33 ERA in 11 games (nine starts)
The rookie’s start on Saturday was his first since Sept. 7, which is why Baker pulled the righty after four innings and 77 pitches. Javier fanned six, which included striking out the side in the first inning. In his last game, he showed a glimpse of what he could provide out of the bullpen, as he struck out five in two scoreless innings of relief last Sunday against the Dodgers.

Because Javier is the most inexperienced of the group, he is almost assuredly headed to a bullpen role in the postseason, where he could be a useful addition. Javier has a tendency to pile up walks, which could be an issue, but when he’s in the strike zone, he’s difficult to square up.

“As far as my role in the playoffs, I’m still not sure what it’s going to be," Javier said. "But whatever they ask me to do, I’m going to be ready to give everything I have to help this team win."

RHP Jose Urquidy: 1-1, 2.70 ERA in three starts
After missing most of the 2020 regular season following a positive test for COVID-19, Urquidy has performed well and is set to make his fourth start in Sunday’s series finale against Arizona. Urquidy has already got an impressive postseason resume, allowing one run in 10 innings in last year’s playoffs, including five scoreless frames in Game 4 of the World Series.

If Urquidy continues to pitch well in his final two starts of the regular season, he is likely to start a game in the Wild Card Series. In a small sample size, he’s been better against left-handed hitters (.329 opposing OPS) than right-handers (.583). The A's, who are closing in on the American League West title and are a potential Wild Card Series opponent for the Astros, hit right-handers well.

RHP Lance McCullers Jr.: 3-2, 4.87 ERA in nine starts
McCullers, who missed all of last season following Tommy John surgery, is likely to start in the postseason if he’s healthy. The righty didn’t record an out in his Sept. 4 start and went on the injured list with a neck nerve irritation. He came back Wednesday and threw seven scoreless innings against the Rangers.

The issue with McCullers is that he hasn’t pitched well away from Minute Maid Park, and the Astros likely won't have any games there in the postseason. (The Wild Card Series will be played at the higher seed and the following rounds will be at neutral sites.) McCullers is 3-0 with a 1.42 ERA and .495 opposing OPS in five home starts and 0-2 with a 13.50 ERA and 1.243 opposing OPS in four road starts.

LHP Framber Valdez: 4-3, 3.82 ERA in 10 games (nine starts)
The emergence of the lefty as a solid big league starter has been one of the best storylines for the Astros this season. He has better control and is now pitching with confidence, becoming a workhorse in the rotation. Valdez has thrown at least seven innings five times, and he held the Rangers to one run in 6 1/3 innings on Thursday

Still, Valdez could be a valuable relief option, like he was Aug. 2 against the Angels when he struck out eight in 6 1/3 innings out of the bullpen. He has one of the best curveballs in baseball and is effective against right-handers (.675 opposing OPS) and left-handers (.595).