Baseball’s best franchise is about to be tested.

When Michael Wacha and Jaime Garcia hit the disabled list with shoulder injuries, the strength of the defending National League champions was challenged. If the team is going to overcome the potentially long-term losses, it will take gargantuan efforts from the remaining 60 percent of the staff and the next men up in the organization.

In the aftermath of Sunday’s victory over the Philadelphia Phillies, Cardinals general manager John Mozeliak alerted the media about Wacha and Garcia, per Jenifer Langosch of MLB.com.

While the idea of the oft-injured Garcia heading back to the sidelines surprised few, the news surrounding Wacha was a bombshell and a major hit to St. Louis’ chances at a postseason berth.

As Mozeliak explained, there’s not a concrete timetable for the return of either starter, leading to worry inside the organization:

It’s concerning. We really don’t know what’s coming. You’re putting two pitchers on the DL today. I’m not in a position where I’ll know when they’re return or how they’ll return or the effectiveness of how they’ll return. It does leave us in a little bit of a gray area. Now, two weeks from now, a month from now, we may feel pretty good about where we are. But as I sit here today, I don’t know that answer.

For St. Louis, the answer lies in two separate but intertwined areas: the remaining rotation members and fill-in starters. 

Let’s start with the trio of Adam Wainwright, Lance Lynn and Shelby Miller. As you can tell from the following chart, St. Louis’ starting rotation is a major reason the team entered play on June 23 having only allowed 256 runs on the season, good for best in the NL and second in all of baseball to the Oakland Athletics.

After a dominant effort—8 IP, 3 H, 0 R, 0 ER, 7 SO, 0 BB—by Lynn against the Colorado Rockies, the numbers are even more impressive for the season.

With 77 games in the books, the Cardinals are on pace to allow just 538 runs for the entire year. To put that into perspective, the last time St. Louis pitching limited opposing offenses to that few runs in a full season was 1968, also known as the year of the pitcher.

While Wainwright and Lynn look poised to carry a rotation over the next few months, worry should accompany Miller’s upcoming starts. On the surface, a 3.56 ERA looks respectable for a 23-year-old starter, but, digging deeper, the numbers aren’t pretty.

With a FIP (fielding independent pitching) well over 4.00 and suspect command, Miller is flirting with disaster on a routine basis. In time, the former first-round pick may develop into an ace or a front-of-the-rotation pitcher. Right now, ERA is the only thing suggesting success thus far in 2014. 

Losing two starters and featuring a young, unproven third starter with spotty numbers isn’t enough to ruin postseason hopes for the Cardinals. Thanks to a deep, fertile prospect base and system-wide depth, the Cardinals have options at the back end of the rotation. 

For the time being, Carlos Martinez will continue to work out of the rotation. In his last start against Philadelphia, the 22-year-old righty earned the victory after tossing up the following line: 5 IP, 3 H, 3 ER, 5 SO, 1 BB.

With a 99 mph fastball and the pedigree of a pitcher groomed to be a starter, Martinez could take off and make folks forget about Wacha, at least for a while. But despite his great stuff and his overwhelming fastball, left-handed batters own an .866 OPS against Martinez this season. If that isn’t corrected, success won’t follow.

In the other spot, Marco Gonzales, last June’s first-round pick, will be called up for a start, per broadcaster Dan McLaughlin. If Gonzales isn’t ready for prime time, Joe Kelly could be back shortly to reprise his role as an underrated starter.

“Joe Kelly, who we believe to relatively close in what we know, still has to check those boxes,” Mozeliak said in regard to rehab for starting pitchers.

Since bursting on the scene as a 21-year-old last summer, Wacha has been one of the best pitchers in the world and virtually irreplaceable. Among starters with at least 155.0 IP since the start of the 2013 season, Wacha‘s 2.79 ERA ranks 12th, per Baseball-Reference (subscription required). 

Among the starters below Wacha on that list: Chris Sale, Cliff Lee, Stephen Strasburg and Max Scherzer

Although Garcia doesn’t possess the same high-end ability, St. Louis lost rotation balance when the southpaw went down. From Wainwright to Lynn to Miller to Martinez to Kelly, the Cardinals rotation could feature five right-handed starters soon. If Gonzales is good enough to hold a spot, the rookie would replace Garcia as manager Mike Matheny’s lone lefty.

Over the next few months, the Cardinals rotation is poised to take a hit. Even if Wainwright and Lynn pitch at a high level, Miller’s uneven season is bound to disappoint, and the combination of Martinez, Kelly and Gonzales isn’t good enough to be trusted for excellence yet.

That being said, not many teams have capable fill-in arms that range from former top-30 prospect (Martinez), first-round pick (Gonzales) and seasoned big-game pitcher (Kelly). 

Before long, St. Louis likely won’t be among the top two or three or five best teams in runs allowed, but there’s enough talent and depth in this system to keep the Cardinals afloat for the next few months. 

Agree? Disagree? 

Statistics courtesy of Baseball-Reference.comFanGraphs and ESPN unless otherwise noted.

Comment, follow me on Twitter or “like” my Facebook page to talk about all things baseball.

Read more MLB news on BleacherReport.com