Houston closer Josh Hader underwent testing on a sore shoulder that kept him out of the Astros' 7-6 win over the visiting Boston Red Sox on Monday.

The ailment arose three days after Hader threw a season-high 36 pitches while getting a win as the Astros defeated the host Yankees 5-3 in 10 innings. Hader didn't pitch on Saturday as New York defeated Houston, then threw in a bullpen on Sunday for a possible appearance but wasn't used as the Astros pulled away late in a 7-1 victory.

"He walked in today and he was doing his (plyometrics) before doing his throwing program and just did not feel right," Astros manager Joe Espada said on Monday. "We went ahead and got some testing done, and we're waiting on the results and should know something more tomorrow."

Hader, 31, is two years into a five-year, $95 million contract. The left-hander earned his sixth All-Star appearance this year and has 28 saves in 29 chances while going 6-2 with a 2.05 ERA. Hader has 76 strikeouts and 16 walks in 52 2/3 innings.

In a career that includes stints with the Milwaukee Brewers (2017-22) and the San Diego Padres (2022-23) before he signed as a free agent with Houston in January 2024, Hader is 227-for-257 on save opportunities with a 34-31 record and a 2.64 ERA. He has 829 strikeouts and 198 walks in 512 1/3 innings.

In Hader's absence on Monday, Houston right-handed reliever Enyel De Los Santos got the last out of the eighth inning and went to the mound in the ninth with a 7-6 lead. He retired the first two batters before yielding a double. Left-hander Bennett Sousa then entered and struck out Roman Anthony to earn his fourth save.