Ben Affleck -- Ravens Are a Nightmare ... But I Believe In the Pats (Video)

Ben Affleck says the Baltimore Ravens are the absolute WORST matchup for his beloved Patriots ... telling TMZ Sports he's got a healthy fear of Joe Flacco.

A pumped up Affleck (seriously, this dude is SWOLL) was leaving Tavern in Brentwood when he told us he wishes Brady and company were facing a weaker opponent this weekend (a shot at the Steelers perhaps?).

Check out the clip ... Affleck breaks down the NFL playoffs and even tells us the teams he fears the most.

But when push comes to shove, Ben says he believes in his boys ... though he wouldn't go as far as his BFF Matt Damon -- who predicted a Super Bowl victory earlier this week.

Stay tuned ...