The team has recalled goalie Malcolm Subban from its AHL team in Providence to replace Gustavsson, who was removed from Tuesday's game due to illness. He was transported to Massachusetts General Hospital and admitted overnight for observation. Preliminary tests came back negative, and he was discharged Wednesday afternoon.
"We placed Jonas on injured reserve as we await his final test results," Bruins general manager Don Sweeney said. "Pending those final test results, he will be cleared for full participation by our medical staff."
The Bruins returned to practice Monday after the All-Star break.
Gustavsson, 31, had a pair of surgeries in 2010 and 2011 for an abnormal heart rhythm when he was a member of the Toronto Maple Leafs.
Boston signed Gustavsson during the offseason to serve as the backup for starter Tuukka Rask. Gustavsson has played in 15 games with a 9-3-1 record, a 2.38 goals-against average and a .915 save percentage.
The Bruins return to action Tuesday when they host the Maple Leafs at TD Garden.