Feeney’s Monza debut ended before he could even cut a lap in the GT World Challenge Europe Endurance Cup race at the famed cathedral of speed.
Feeney joined AlManar Racing by GetSpeed duo Al Faisal Al Zubair and Dominik Baumann in a Mercedes-AMG GT3 for the three-hour race.
However, their campaign lasted less than 20 minutes as Al Zubair was involved in a Lap 6 crash.
The incident caused significant damage to the left front, forcing Al Zubair to retire the car to the side of the road.
All three GetSpeed entries suffered DNFs in a race won by the all-Bronze line-up of Ahmad Al Harthy, Sam De Haan and Jens Klingmann for OQ by Oman Racing.
It marked the first time in GT World Challenge Europe history that a team outside the Pro ranks won outright.
While Feeney failed to feature at Monza, Mostert at least made it to the finish line at Indianapolis.
The SunEnergy1 Racing driver joined Kenny Habul and Jordan Love in the Battle on the Bricks, also sharing a Mercedes-AMG GT3.
The trio were in contention for a GTD Pro podium heading into the final hour but had their hopes dashed when the former race-leading Acura AR-06 of Louis Deletraz sideswiped Mostert.
The two-time Bathurst 1000 winner went sliding through the grass and wound up finishing seventh and more than 50 seconds off the lead.
Michael Christensen and Laurin Heinrich took GTD Pro honours for AO Racing while BMW factory outfit Rahal Letterman Lanigan Racing won outright with Phillip Eng and Jesse Krohn.
LMP2 honours went to New Zealand’s Hunter McElrea alongside Mikkel Jensen and Steven Thomas.