By FOX Sports staff
The 34-year-old only recently signed for Heart from Dutch giants PSV Eindhoven and was making his first appearance in Sunday's pre-season friendly against Brisbane Roar, which ended in a 3-0 loss.
However, to make matters worse, Engelaar limped off just before the half-hour mark after getting into a heavy collision with Thomas Broich and coach John Aloisi admitted he feared the worst after the game.
And on Monday, the club confirmed on their official website that the Dutchman had indeed suffered a fracture and would be flying back to Melbourne "to undergo further medical assessment".
Heart also revealed that no further comment will be made until a full diagnosis had been completed by their doctor and medical staff.
Engelaar, who had a brief stint in the German Bundesliga playing for Schalke, won 14 caps for Netherlands and represented them at Euro 2008.