The legendary kicker tells TMZ Sports ... he believes Tucker's just simply hit a rough patch -- and he's confident the 35-year-old will fight his way through it in time for Baltimore's impending playoff run.

"He's going to snap out of it," the former Buccaneers kicker said. "There's no question that he knows how to kick. He's done it forever."

Tucker -- normally the most consistent kicker in the NFL -- has made just 19 of his 27 field goal attempts this year ... and he's uncharacteristically missed two extra points as well. In fact, the three misfires he had against the Eagles on Sunday arguably cost his team a big win.

John Harbaugh, though, has said he'll stick with his guy for the foreseeable future ... and Gramatica says that's "100 percent" the right move.

"It would be like telling Tom Brady, 'Look, you're struggling now for a season,'" Gramatica said. "'We're going to bench you or find somebody else.' You can't. He's the Tom Brady of kicking. He's that guy. You have to let him work through it."

As for what's causing the newfound yips, Gramatica says in his opinion, it just simply has to be something physical that's momentarily thrown his mechanics out of whack.

"He's mentally one of the strongest, toughest guys I've ever watched play in the NFL," he said. "So, I don't think it's a mental thing."