The right-hander appeared in four games during the first week of the regular season. Manager Dusty Baker said Pressly had been bothered by the soreness for a couple of days and the team sent him back to Houston for additional examination.
Pressly's velocity had been noticeably down during his first few appearances, but Baker didn't think the knee issue was a factor. Pressly was 0-1 with a 2.70 ERA and three saves to begin the season.
"I asked him and he said he didn't think it did. That's your shove off leg, too," Baker said. "He's a tough guy and he's not going to make excuses. Like I said, we've just got to get him right."
Houston selected left-hander Parker Mushinski from Triple-A Sugar Land to take Pressly's roster spot. Mushinski will make his major league debut when he makes his first appearance.
Designated hitter Yordan Alvarez was also back at the ballpark after missing several days with a non-COVID illness. Baker said Alvarez would go through the pregame workout and then be assessed on when he may return to the lineup.