Good news, Niners fans ... former San Francisco DB Donte Whitner says he's expecting a walk in the park for his ex-team on Sunday -- telling TMZ Sports the 49ers will beat the Lions by more than three touchdowns!!
Whitner says he's anticipating the final score to be 37-14 ... and it's all, in part, due to his confidence in Brock Purdy -- who he says is a top three or four quarterback in the NFL right now.
"I'm not expecting it to be close," Whitner said of the NFC Championship Game.
Of course, Purdy and the Niners didn't look their best last weekend against the Green Bay Packers ... they needed a late score in the fourth quarter to pull out the win despite being a heavy favorite heading into the game.
But, Whitner tells us he thinks the rain played a huge role in that ... promising, "You won't see that same 49ers football team this week vs. the Detroit Lions."
Whitner -- who logged snaps for the Niners from 2011 to 2013 -- also praised the hell out of Purdy during our conversation ... saying he has no idea why the 24-year-old signal-caller gets so much criticism from national pundits.
"When I go back and I analyze the film on Brock Purdy, he does everything you want him to do as a quarterback," Whitner said.
"How can you continue to beat this kid down when he was the last pick in the draft and he's shown all the qualities and capabailities to be a top franchise quarterback."
Kickoff for the big game is slated for 3:30 PM ... and while Whitner will certainly be watching -- given his faith in his old team, don't expect him to be sweating much!