Sinkhole, Schminkhole ... the San Francisco 49ers aren't sweating that crater that opened up on the football field last weekend -- telling TMZ Sports it "happens all the time in football" ... so, no big deal.

You know the story ... Ravens kicker Justin Tucker missed a 45 yard field goal after the Levi's Stadium ground crumbled under his plant foot ... causing some to doubt the quality of the field.

Who's not concerned? The 49ers -- 'cause a rep for the team tells us issues like Justin Tucker mystery hole -- which he insists is NOT a sinkhole -- are just a part of the game.

"I ensure you this type of thing happens all the time in football," a team spokesman told us, "with around 140 plays, the ground loosens up with wear and tear."