Nolan Arenado left Arizona's game with trunk discomfort, expects MRI

Nolan Arenado left Arizona's 5-3 loss to Atlanta on Sunday with what the club described as left trunk discomfort, and the third baseman told MLB.com's Rick Farlow and other reporters afterward that he would probably get an MRI. Arenado said he was worried, and the reason was straightforward: he had never felt this type of soreness before.

The injury introduces roster uncertainty for a Diamondbacks club sitting 10 games back in the National League West but riding a three-game winning streak and heading into a three-game series at Fenway Park beginning Monday.

What happened

Arenado told reporters he first noticed something while fastening his leg guard before stepping in for his fourth-inning at-bat. The sensation did not register immediately as sharp pain, he said, but when he swung the bat it did not feel right. He grounded out to third base and looked uncomfortable running toward first, per MLB Trade Rumors. He was replaced in the field shortly after.

In his own words to reporters, Arenado described a soreness in the intercostal area — the region between the ribs — that he could not quite characterize. He said the discomfort was not getting drastically worse during the swing, but the unfamiliarity was enough to prompt his exit. He told reporters he did not want to mess around with it, which is the kind of sentence that tends to precede an injured-list transaction rather than a lineup card appearance.

The intercostal muscles are involved in trunk rotation and breathing mechanics, both of which are fairly central to the act of hitting a baseball. Arenado's acknowledgment that he had not experienced this sensation before, combined with his stated worry, suggests the club will proceed carefully — particularly with imaging likely in the coming days and a road trip already underway.

Why it matters

Per MLB Trade Rumors, an injured-list stint is possible. The Diamondbacks have not announced a timeline, and Arenado's availability for the series opener at Boston on Monday is unconfirmed. No corresponding roster move had been reported at the time of the story.

The timing matters operationally. Arizona is in the middle of a pennant-race calendar that does not accommodate extended diagnostic uncertainty. The club will need imaging results before it can make decisions about roster construction, and the Boston series begins before those results are likely to be public. A third baseman who exits a game mid-inning after grounding out, cites unfamiliar pain, and tells reporters he is worried is not a third baseman the club can pencil in with confidence for Monday's lineup.

Under general league rules, a position player placed on the injured list must remain there for a minimum of 10 days. The September expansion to 28 active roster spots is still roughly two weeks away, which means any replacement would come from the current 26-man group or require a corresponding move to create a spot.

Where the club stands

Arizona is 77-68 (.531), second in the NL West and 10 games behind the division leader. The Diamondbacks have won three consecutive games and open a three-game series at Fenway Park on Monday, with Mitch Bratt scheduled to face Alec Gamboa. Merrill Kelly is lined up for Tuesday against Ranger Suarez, and Brandon Pfaadt is slated for Wednesday opposite Payton Tolle.

A three-game winning streak is a reasonable moment to absorb difficult news — the club has some momentum and the schedule has not yet turned punishing. But Fenway Park in August is not the place to carry a roster question unanswered, and the Diamondbacks will be managing Arenado's status in real time as the series unfolds.

What we don't know yet

The club has not announced whether Arenado will undergo the MRI on Monday, what the imaging might reveal, or whether he will travel with the team to Boston. His availability for any game in the Fenway series is unconfirmed, and no injured-list placement has been reported as of the MLB Trade Rumors story.

The range of outcomes for this type of injury is wide. Arenado's visible discomfort running the bases and his decision to exit rather than continue suggest the club will wait for imaging before offering any public prognosis. His own uncertainty about what he felt — describing the sensation in the intercostal area while also saying he simply did not know what it was — is the most honest summary of where things stand. That uncertainty belongs to him, not to the diagnostic process, which has not yet produced results.

What to watch

The MRI results will determine Arenado's immediate availability and whether the Diamondbacks need to make a roster move before or during the Boston series. If the imaging reveals a structural concern, the club would face a decision about whether to place him on the injured list and recall an infielder to cover third base.

Arenado's status for Monday's opener is the most pressing question. The next public update will likely come through a pregame availability announcement or a formal roster transaction — whichever arrives first. The club has not indicated a contingency plan, and the roster construction heading into the final stretch of the regular season will depend on what the imaging shows and how Arizona chooses to respond.

Per MLB Trade Rumors, an IL stint remains a possibility — not a certainty, but enough of one that the Diamondbacks will be watching the results as closely as anyone in the NL West standings.