ST. PETERSBURG -- Bryan Woo’s frustration was palpable as he paced off the mound in the fourth inning on Monday night at Tropicana Field, once again earlier than anticipated within a season in which his health has been the leading topic of discussion every time he takes the mound.

The electric right-hander experienced right hamstring tightness that led to enough discomfort that he couldn’t complete a warmup pitch to remain in the game -- a 4-3 loss to the Rays -- halting himself as he lumbered down the mound with his delivery before releasing the ball to the plate.

Woo then sunk his head into his glove before slowly pacing off the hill, an expression telling of his trying season. Unavailable to media postgame, Woo will undergo an MRI on Tuesday, and the Mariners are uncertain if the injury will necessitate an IL stint.

“Initial look is we'll just have to see,” manager Scott Servais said. “It's hard to project anything there. We just have to get an MRI tomorrow and see where we're at.”

Making the night sting even more was that Seattle blew a two-run lead in the eighth inning, which all began with a two-out walk from Austin Voth to .111 hitter Taylor Walls with the bases empty. Voth then surrendered a single to Jose Siri and a ground-rule double to Ben Rortvedt to make it a one-run game, after which Andrés Muñoz was summoned.

Muñoz walked his first batter, old friend José Caballero, in a full count, then gave up the go-ahead dagger to Yandy Díaz, an awkward chopper that sailed over Ty France as Caballero was running in front of him, which led to two runs.

“It just goes back to the little things,” said Cal Raleigh, who crushed a 110.1 mph solo homer in the fourth and advanced to 3-for-3 on steal attempts in the sixth. “Today, it's the two-out walk -- it killed us. That was kind of the key to the game there. Credit to them, they put bat to ball after that. We got the ground ball at the end -- it took that hop, unfortunately.”

As for Woo, Servais said that it was the first time that the right-hander experienced any lower-body injury.

Woo missed the first six weeks of the schedule due to right medial elbow inflammation, exited early in his 2024 debut after his forearm tightened up on him, skipped a June 11 start due to the issue, underwent an MRI for it after -- which came back clean -- then was admittedly rusty in his first start back last Wednesday in Cleveland.

Which made Monday all the more dispiriting, given that Woo looked like his best self, with a huge spike in velocity on both his fastballs. The sinker was 2.2 mph up from his season average and the four-seamer was up 2.3 mph, both consistently topping 97 mph.

Woo surrendered just five hits and one run, which was manufactured immediately after he exited when Tayler Saucedo sailed a pickoff attempt on Richie Palacios, Saucedo's inherited runner at first base, then spiked a wild pitch that allowed him to score.

“Nobody likes playing hurt,” said Raleigh, who is roommates with Woo. “You're trying to avoid injuries, and when new ones pop up like that, it can get really frustrating. So I feel for him. Hopefully, it's nothing major and he can turn around really quick. But I know he's been working hard to get back, and he was looking really good tonight.”

Monday marked only the second Mariners loss in 36 games in which they’ve led after the seventh, and overall, it was their fifth loss in seven games on this three-city road trip. Seattle is now 18-24 on the road and has seen its lead in the American League West trim from 10 games at the beginning of the trip to 5 1/2.

Woo’s next scheduled turn is Sunday against the Twins in Seattle, but the club has an off-day on Thursday that it could ostensibly use to re-slot the rotation.

Emerson Hancock has been Woo’s fill-in when needed and is expected to start on Saturday for Triple-A Tacoma, after himself exiting early in his start for the Rainiers last Wednesday with lower back pain. Jhonathan Diaz, who made the spot start for Woo on June 11, last pitched on Saturday for Tacoma and was hit hard for five runs (four earned). Veteran Dallas Keuchel is another option, having most recently pitched on Friday.

If Woo does need an IL stint, the more pressing need will be for bullpen reinforcements to get through these final two games at Tampa Bay, especially after the Mariners used all but Cody Bolton and Eduard Bazardo on Monday.