The Phillies have cracked the case of Didi Gregorius’ missing power. Finding a solution will be trickier.

When Didi Gregorius went on the injured list earlier this season, he hadn’t hit a home run yet. He has been back in the Phillies’ lineup for a month, and still, he hasn’t gone deep. It’s the second-longest homerless stretch of his 11-year major league career.

The Phillies believe they have cracked the case of Gregorius’ missing power. Finding a solution will be more difficult.

Interim manager Rob Thomson revealed Sunday that Gregorius is dealing with lingering pain from the sprained left knee that caused him to miss 28 games in May and early June. The 32-year-old shortstop received an injection of what Thomson described as “lubricant” after Friday night’s game and wasn’t in the lineup Saturday or Sunday night against the St. Louis Cardinals.

» READ MORE: As the Phillies forge ahead without Bryce Harper, Pat Gillick recalls 2007 trade for Chase Utley’s fill-in

“I think it’s sort of been building over time ever since he came back from it,” said Thomson, who didn’t rule out a return to the injured list but said the Phillies also won’t have a definitive answer for another few days.

At a minimum, it appears Gregorius will have to manage his knee pain for the rest of the season. And that’s a problem because Thomson and hitting coach Kevin Long agree that the injury has sapped lefty-swinging Gregorius of his extreme pull-side power.

“I would think so,” Thomson said. “Staying on his backside, turning on it to the pull side, hopefully this [injection] clears it up and he gets pain-free and can start pulling the ball the way he normally does.”

All of Gregorius’ 133 career home runs have been hit to the right of center field. But because the injury is to the knee on his back leg, he has been unable to generate power by turning on the ball. More than half of his 36 hits this season, including a triple last week against the Atlanta Braves, have gone the other way to left field or left-center.

Gregorius has gone 155 plate appearances this season without hitting a home run. Entering play Sunday, only six players — Washington’s César Hernández (351), Cleveland’s Myles Straw (310), the Yankees’ Isiah Kiner-Falefa (257), Kansas City’s Nicky Lopez (244), Colorado’s Yonathan Daza (217), and Detroit’s Tucker Barnhart (157) — had longer dry spells to begin the season.

Not since his second and third full seasons in the majors has Gregorius gone longer without hitting a home run. The last time he hit a ball that landed on the other side of the fence: Sept. 21, 2021, 181 plate appearances ago. He went 220 plate appearances without a homer from Aug. 24, 2014 to May 20, 2015.

» READ MORE: Mickey Moniak will get his best (and last?) chance to show the Phillies he belongs

It’s a problem for the Phillies, and the absence of Bryce Harper for at least six weeks with a broken left thumb only makes it more glaring. It also explains why lefty-hitting Darick Hall has batted cleanup in all four of his starts since getting called up from triple A. Gregorius’ power outage has turned Hall into the Phillies’ second-best left-handed power threat behind Kyle Schwarber.

But as long as Gregorius can avoid the injured list, he’s going to play. Thomson noted improved defense, although he still ranks as a below-average shortstop in defensive runs saved. Gregorius also has the ability to get hits the other way, even if they’re mostly singles.

The Phillies also don’t have many alternatives. They remain hopeful that rookie Bryson Stott may be their future shortstop. He filled in Sunday night for Gregorius but has been playing mostly second base since Jean Segura went down with a broken right index finger.

Utility infielder Johan Camargo, who has been out with a right knee strain, is eligible to come off the injured list Wednesday. He could be an option. Recently recalled Yairo Muñoz is another possible shortstop fill-in.

The Phillies also may explore acquiring a left-handed hitter before the Aug. 2 trade deadline. The expectation around baseball is the Kansas City Royals will trade outfielder Andrew Benintendi. The Arizona Diamondbacks could move outfielder David Peralta.

But issues are mounting with other areas of the roster. The starting rotation, for example, may require reinforcements after Ranger Suárez (lower back spasms) joined Zach Eflin (bruised right knee) on the injured list Sunday.

» READ MORE: The Braves won it all without Ronald Acuña Jr. Can the Phillies even make the playoffs after losing Bryce Harper?

Everything will be a little easier if Gregorius is able to plug his power back in. But it all comes down to getting his knee healthy.

“The offensive power numbers haven’t been there, but his at-bats have been good and he’s able to hit the ball the other way,” Thomson said. “His defense has been outstanding. Just for that alone, I want him on the field.”