CC Sabathia's right knee is hurting once again, leaving the Yankees' rotation thin and raising questions about whether or not the former ace is at the end.

CC Sabathia has scuffled this year, and by the look of it, he may have thrown his last pitch for the 2015 season—or even longer. On Sunday at Yankee Stadium against the Indians, he struggled mightily to throw strikes, then took himself out with two outs in the third inning after notching his only strikeout (against four walks) due to what The New York Times's Tom Pedulla described as "stabbing pain" in his right knee. While Sabathia will undergo an MRI on Monday, a disabled list stint appears to be a foregone conclusion.

UPDATE: The Yankees have indeed placed Sabathia on the DL with "right knee inflammation." No timetable has been provided for his return, though manager Joe Girardi admitted that it's possible Sabathia's season is over.

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After more than 3,300 professional innings, the warranty on Sabathia’s right knee—the one on which his 300-some-pound bulk lands on every pitch—has long since expired. He underwent off-season surgery to repair a torn meniscus following the 2010 season, and the joint limited Sabathia to just eight starts last year before he required another surgery, this one to remove a bone spur. Last August, ESPN New York's Danny Knobler reported that while Sabathia had avoided microfracture surgery, doctors told him that he had almost no cartilage under his kneecap, and that the knee would require frequent maintenance involving platelet-rich plasma injections and draining of fluid to reduce the swelling. At that point, he received an injection of cortisone and stem cells in hopes of reversing the degeneration.

Sabathia's regimen of maintenance, which has included two fluid drainings this season as well as a recent cortisone shot, has allowed him to start 24 times this year, tied with Nathan Eovaldi for the team high, but the results haven't been there for the 35-year-old lefty. Via Brooks Baseball, while his velocity has rebounded by about one mile per hour over last year, his 91.5 mph average for his four-seam fastball and 90.6 mph for his sinker are both down more than three miles per hour from 2011. He's been tagged for a 5.27 ERA and 1.7 homers per nine, both of which rank as the AL's second-highest mark among qualifiers. Even with a 3.1 strikeout-to-walk ratio, his 4.82 FIP is the league's third-highest, and his 38% quality-start rate is tied with Eovaldi for the AL’s fifth-lowest.

As dismal as those numbers are, Sabathia's recent performance had offered glints of optimism, as he had pitched at least six innings in each of his previous three starts, allowing just one homer and seven runs over a combined 18 2/3 innings against the Red Sox, Indians and Twins. Via NJ.com's Brendan Kuty, while he had babied the knee earlier this season, altering his landing spot to minimize the impact, his velocity had spiked recently, more or less coinciding with the improved results, because of a change:

Sabathia said he was "just saying, 'Screw it'" and letting it fly. That, he said, is probably when the pain started. …"What else is there to do?" he said. "Pitch how I've been pitching or go out there and try to compete? So I decided to give it everything I had."

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​Sabathia is making $23 million this year and is under contract for $25 million next year, with a $25 million vesting option for 2017 that can void under only a few conditions pertaining to a shoulder injury; if it's his knees or even his elbow (which required bone spur surgery after the '12 season) or another part of his body, the Yankees are still on the hook. As the unquestioned ace of the rotation, his performance helped the team win a championship back in '09, and he earned All-Star honors and top-four finishes in the AL Cy Young voting three times apiece in his first four years in pinstripes, during which he averaged 226 innings with a 3.28 ERA (135 ERA+). Since then, he’s been roughed up at a 5.01 ERA clip over an average of 132 innings per year, largely due to a swollen 1.5 homers per nine. He's tried reducing his considerable weight to reduce the stress on his knee, but he felt weaker, and his velocity waned. Barring some extraordinary rebound via microfracture surgery or some other procedure, the Yankees will have to plan around the likelihood that his contributions could be minimal going forward, and he could be a sunk cost entirely.

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More pressing is the short-term concern. With three losses out of four against the Indians this past weekend, the Yankees (68–55) slipped half a game behind the Blue Jays (69–55) in the AL East race; while New York still has a four-game cushion for the top wild-card spot, the Bombers have seen their seven-game division lead evaporate in less than four weeks. General manager Brian Cashman, meanwhile, did little to revamp the roster, while the Blue Jays added David Price, Troy Tulowitzki and others prior to the July 31 non-waiver trade deadline.

Last week, the Yankees began a shift to a six-man rotation by giving rookie Bryan Mitchell a spot start on Monday against the Twins, but he suffered a small nasal fracture and a concussion when he was hit by a line drive off the bat of Eduardo Nunez. Fortunately, he could be back soon; he’s slated to throw a simulated game in Tampa on Tuesday. Michael Pineda, who has been out since July 24 due to a forearm strain, is slated to return on Wednesday against the Astros, about a week ahead of schedule. Manager Joe Girardi could slot both into the rotation alongside Eovaldi, Ivan Nova, Masahiro Tanaka and rookie Luis Severino in order to provide a bit of extra rest for each starter, but that group offers no guarantees.

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​Tanaka, who has pitched through a small tear in his ulnar collateral ligament, can't seem to remain sharp in back-to-back starts; he has a 3.61 ERA (109 ERA+) but a 4.11 FIP. Nova, who has made just 10 starts since returning from Tommy John surgery, has similar numbers (3.72 ERA, 4.12 FIP) but has been downright erratic, as his 40% quality-start rate testifies. Eovaldi (4.24 ERA, 3.53 FIP) is an innings-eater who can't seem to take the next stop forward, whiffing just 6.6 per nine despite fastball velocity that can reach triple digits. Pineda has the best peripherals if not the best results among the Yankees' starters, as his 3.99 ERA and 3.00 FIP attest. Severino, who has delivered a 2.74 ERA through his first four starts, has a high ceiling and no concerns about an innings limit, but he's just 21 years old. The 24-year-old Mitchell offers promise, but he has just 32 big-league innings and three starts under his own belt. As a unit, the rotation's 4.25 ERA ranks just 10th in the AL, their 3.99 FIP sixth—good enough to get by when the Yankees' offense, which ranks second in the league in scoring at 4.76 runs per game, is humming, but a liability if not.

Cashman doesn't expect to make a waiver deal before the Aug. 31 deadline, nor does it appear likely that Adam Warren will return from the bullpen. Warren made 14 starts with a 3.59 ERA in the first half of the season, which stands as a team low aside from Severino, but his 5.9 strikeouts per nine, 4.16 FIP and 43% quality-start rate attest to his wobbliness in that role. He's been much stronger in relief (1.75 ERA, 2.15 FIP, 9.1 strikeouts per nine) in front of Dellin Betances and Andrew Miller, and with the length of nearly every start from the aforementioned group a concern, it’s understandable why the Yankees want to leave him in place.

As their playoff hopes go, the Yankees will have to make do with the parts on hand. They can only wait and see with regards to their former ace.