Chicago Cubs center fielder Albert Almora Jr was left in tears at Minute Maid Park on Wednesday after a hard-hit line drive flew into the stands and struck a girl.
The girl, whose identity has not been disclosed, was later taken to hospital, according to a statement from the Astros. Local media reports said the girl was not seriously injured.
Almora meanwhile was badly shaken by the incident, needing to be consoled by several players from both sides and sobbing into the arms of a security guard at one point.
"I had to try to keep my composure during that at-bat, but when that half-inning was over, I just couldn't hold it anymore," Almora told reporters after the game.
The incident was similar to an accident at Yankee Stadium in 2017 when a toddler was injured by a foul ball.
The Yankees later took the decision to expand the coverage of protective netting beyond MLB guidelines which existed at the time.
Major League Baseball recommended clubs expand safety netting to at least the far end of each teams' dugouts in time for the start of the 2018 season. The area where the girl was hit in Houston on Wednesday was around 10 feet past the visiting teams dugout.
MLB described the latest fan injury as "extremely upsetting" in a statement on Thursday, adding that the issue was under constant review.
"We send our best wishes to the child and family involved," the league said. "Clubs have significantly expanded netting and their inventory of protected seats in recent years. "With last night's event in mind, we will continue our efforts on this important issue."
However the latest incident showed that existing safety standards remained inadequate according to a woman, whose mother died after being hit by a foul ball at Dodger Stadium last August.
Jana Brody told ESPN's Outside the Lines program that MLB's failure to order a greater expansion of netting zones was "unconscionable."
"It's unconscionable that fans are still getting hurt by hard-hit foul balls and MLB has not increased the netting requirements, even after a foul ball caused a brain hemorrhage and my mom's death in August at Dodger Stadium," Brody told ESPN.
"We see not only the fans, but the players are traumatized by the horror and damage. At least the players earn millions of dollars and they can afford therapy for their trauma."