The ice pack on James Paxton’s left knee was as bulbous as a watermelon and just as cumbersome as he hobbled across the clubhouse Sunday morning. The Yankees hurler plopped down on a couch in front of the high-definition televisions and began following his doctor’s orders: rest.

That’s no easy request, considering that Paxton was being counted on to replace the injured Luis Severino at the top of the rotation. But like so many other Yankees this season, Paxton is on the sidelines hoping for a speedy recovery, wondering what went wrong.

Despite his ability to overwhelm hitters, Paxton is no stranger to breakdowns. The left-hander never threw more than 160 ⅓ innings in six seasons with the Mariners, sustaining injuries to a forearm, an elbow, a pectoral muscle, a latissimus and a left finger. But the knee had never been a problem for Paxton, at least not before he made four starts in the Bronx in 2019.

Is there a connection? Paxton believes there might be. After brainstorming with the pitching coach Larry Rothschild and some of his fellow pitchers, Paxton suspects the mound’s hard, sticky clay could be the culprit. He theorizes the lack of “give” is irritating the knee as it rotates upon release of the ball. It’s only a hypothesis, but the Yankees seem willing to indulge Paxton. They plan to sprinkle a softer, looser compound near the rubber when Paxton returns from the injured list, which will allow for freer movement.