Luke Weaver and Jack Flaherty will get a chance in September to prove they should be in the Cardinals' starting rotation in 2018. (File)

By Rob Rains

The Cardinals enter September on the fringe of the NL Central race, not really playing well enough to convince observers they can catch the Cubs but at the same time still close enough in the standings to know that it is possible.

Whether that happens or not, the clock already has begun ticking toward 2018 with the team’s decision to trade Mike Leake and promote Jack Flaherty, who will make his major-league debut on Friday night in San Francisco.

Flaherty is just one of the players who begin September knowing that how well they play in the season’s final month will be a factor in the Cardinals’ off-season evaluations as they begin planning for next year.

With that in mind, here are the 10 players with the most to prove in September:

Luke Weaver – An injury to Adam Wainwright opened a spot for Weaver in the rotation and he has responded with back-to-back 10-strikeout games, the first rookie to achieve that feat since Rick Ankiel in 2000. More important than the strikeouts, however, was the fact he allowed a total of two runs in those two starts in a combined 12 2/3 innings. Weaver likely will make five or six more starts this season and if he continues to pitch well should lock up a spot in the 2018 rotation.

Carlos Martinez
– Expected to be the leader of the rotation, this has been an up-and-down season for Martinez, mixed with good starts and poor outings. By pitching well down the stretch – and solving his first-inning troubles – Martinez can go a long way to re-establishing himself as the staff’s ace and a pitcher the Cardinals can count on to lead the staff going forward. A poor month, however, would no doubt create some concerns about how much he can be counted on in 2018 and beyond.

Randal Grichuk
– The Cardinals have acknowledged that just as they have an abundance of young pitchers on the cusp of the major leagues, the group of outfielders converging on the majors is just as crowded. That means somebody, or more than one, is going to be moved this winter and Grichuk could be one of the candidates. He has shown flashes of his power this season, again, but still has fallen into major ruts where he can’t get a hit and strikes out way too often. He needs a solid September not only to try to convince the Cardinals he could have a role on the team next year but to build up interest from other teams as a trade candidate if he does not fit into the Cardinals’ plans.

Jack Flaherty
– While the trade of Leake opened the first door for Flaherty, he needs to pitch well in September to convince the Cardinals he can begin next season in the rotation. How many spots the team will be looking to fill depends on what happens with Lance Lynn, how well Wainwright can come back from his latest injury and whether Alex Reyes is well enough to begin next year in the rotation. There could very well be a spot for Flaherty, especially if he has a good September.

Tyler Lyons – From seemingly being ignored for virtually the entire first half of the season, Lyons has emerged in the second half as the Cardinals’ most reliable reliever. He has worked 16 innings since the All-Star break and not allowed a run, giving up just three hits in 48 at-bats. The injury to Trevor Rosenthal has elevated Lyons into at least a share of the closer’s role, and with the team in need of somebody to fill that spot next year too, a good September could go a long way to keeping him in the running for that job.

Stephen Piscotty
– This has been a season to forget for Piscotty, who didn’t know his season highlight was going to come right as the year began when he signed a contract extension. The Cardinals are willing to give Piscotty a pass on this year because of all that he has been through with his mother’s illness, but closing the year on a positive note would give him something to build on this winter as he regroups for 2018. He probably is not in as much danger as Grichuk of losing his job to a younger outfielder, but the possibility his name could come up in trade talks this winter cannot be dismissed.

Brett Cecil
– On the list of the Cardinals’ biggest disappointments this season Cecil has to be near the top. After giving him a four-year, $30 million contract, he was expected to be dominating out of the bullpen but it never happened. Like Piscotty, a productive final month would not salvage the season but would at least give him and the team some encouragement that 2018 can’t possibly be as bad as this year.

Michael Wacha – With the Cardinals committing to the youth movement for next year’s rotation, there might be only one spot open for a veteran – as of now either Wainwright or Wacha. How Wacha pitches in September could influence the decision, with whichever pitcher is not in the rotation perhaps being moved to the bullpen. Wacha has been mentioned as a candidate for that role in the past, primarily because of how well he has done in the first inning and in a team’s first time through the batting order. He could perhaps become that hybrid reliever the Cardinals have talked about in the past, someone who could come in and throw at least two innings.

Aledmys Diaz – After losing his starting shortstop role to Paul DeJong just a year after making the All-Star team, Diaz is hoping to return from Memphis in September and get some chances to show that he can still hit and be effective in the majors, even if it is in a backup role. He has played both third base and second base during his time in Triple A and hopefully the Cardinals will give him a chance to play his way back into consideration for a role on the team for 2018.

Luke Voit – The injury to Jedd Gyorko opened the door for Voit to get a couple of starts at first base, with Matt Carpenter moving to third, but he might not have many more chances like that in September. Voit has proven to be an effective pinch-hitter since his promotion to the majors, and that likely will continue to be his primary role in the final month of the season. Succeeding when he gets the chance, either starting or coming off the bench, will be the best way for Voit to keep himself viable as a candidate to make the team next year.

Follow Rob Rains on Twitter @RobRains