Paulino, making his eighth start of the season, suffered the injury throwing a pitch to Pirates pitcher Ian Snell. He pitched 1 2/3 innings, allowing three hits and one run and striking out four of the eight batters he faced, leaving with the Astros trailing, 1-0.
He was examined by team medical director David Lintner.
"He told me it was going to be day-to-day," said Paulino, who missed all of last season with an arm injury. "We'll see what happens tomorrow and the next day. Now, I feel a little strained. Hopefully, it will get better."
Astros manager Cecil Cooper said Paulino felt a little discomfort in the groin area while he was warming up in the bullpen, but after he warmed up and stretched it out, he thought it was going to go away.
"He was able to go, and that one pitch he kind of pulled it a little more," said Cooper, who thought the hard-throwing Paulino had "electric stuff."
Paulino took the injury in stride.
"When something like that happens, it happens," he said. "I was throwing pitches for strikes, and after that I felt stiffness in my groin. When I threw to the pitcher, I felt a little pain and said, 'OK, that's enough for me.'"
The bullpen picked up Paulino and the Astros by holding the Pirates to three runs over 7 1/3 innings, led by Russ Ortiz throwing 4 1/3 scoreless frames.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.