The Boston University men’s hockey team finally has a number-one goaltender, but not by choice.

Freshman Matt O’Connor is out indefinitely with spontaneous pneumothorax and is expected to make a full recovery, according to a team source. Spontaneous pneumothorax is a collapsed lung that happens with no apparent cause.

O’Connor is in the hospital. There is no information available on a recovery timeline.

“A small area in the lung that is filled with air can break open, sending air into the space around the lung,” according to the U.S. National Library of Medicine. Tall, thin people are more likely to suffer collapsed lungs.

The 6-foot-5, 201-pound O’Connor has posted a .910 save percentage and 2.86 goals-against average in 19 games (18 starts) in his rookie campaign.

The news comes two days after freshman Sean Maguire started two games in a weekend for the first time this season. After making 49 saves and allowing one goal in a win against the University of Vermont Friday night, Maguire gave up four goals the next night, just hours after finding out he would make the start.

BU coach Jack Parker said after Saturday’s game O’Connor had trouble breathing during the pre-game skate Saturday afternoon, and the team made the decision to hold him back shortly thereafter.

Maguire, whose .914 save percentage and 2.95 GAA in 15 games are quite comparable to O’Connor’s numbers, is in line to be the team’s regular goalie.

Annie Maroon contributed to this report.