The actor's latest offering, "The Fall Guy" -- which was getting heavily promoted in recent weeks -- had a disappointing box office opening weekend -- having raked in just $28.5 million domestically ... this after projections had it pegged for between $30 and $40 mil.

Overseas, 'TFG' made an extra $25.4 mil ... bringing its total debut haul to around $65M.

It might not sound like that bad of a return on its face ... but considering how much it cost to produce this film, it ain't good news for Universal -- the studio that distributed this film.

The reported budget for "The Fall Guy" was about $140 million -- not to mention all the marketing that went into hyping it up beforehand ... so yeah, a pretty pricey investment.

With that said ... not all hope is lost for RG and co. -- 'cause the director for this action movie, David Leitch, put out another big-budget blockbuster, "Bullet Train," a couple years back that also started out slow ... but which picked up steam as the weeks went on.

That movie only cost $90 mil to make, and while it only brought in about $30 mil domestically in its opening weekend ... 'BT' walked away when it was all said and done at $239 million.

Bottom line ... 'Fall Guy' can still earn its budget back, but with a few big hitters coming to theaters in the coming weeks -- including another 'Planet of the Apes' movie -- time will tell if people care about watching Gosling play a stuntman with splashy explosion scenes.