Murphy, who has started all 34 games for the Giants so far this season, picked up a groin injury in his side's dramatic comeback win against Coventry Blaze over the weekend.
And, having been assessed by medical staff, he's now been ruled out of action indefinitely.
"We have been hit hard with injuries as of late, and losing Murph could have been disastrous," Giants general manager Todd Kelman said.
But the Giants have moved quickly to secure the services of Canadian Garrett Zemlak, who'll now make his debut in Belfast on Wednesday night against one of his former clubs - the Fife Flyers.
The 23-year-old Saskatchewan native enjoyed great form with the Flyers, but a summer move to the Braehead Clan didn't pay off and he was released from his contract earlier this month.
"We're happy that we were able to agree to terms with Garrett before he headed back to North America," Kelman added.
"He had a few options in leagues over there, but he wanted the opportunity here in Belfast and is looking forward to making his debut tomorrow night."
Another player added to the Giants' injury list is defenceman Sam Roberts, also now out indefinitely.
He took a hit early on in that weekend game against Coventry and a scan has since revealed a broken collarbone.
Face-off in Wednesday's game between Belfast Giants and Fife Flyers at the Odyssey is at 7.30pm.