Sorry, Boston ... Roger Clemens is predicting a MONSTER career for Gerrit Cole with the New York Yankees, telling TMZ Sports, "It's gonna be great, man."
Cole just inked the fattest contract EVER for a pitcher ... signing a 9-year, $324 MILLION deal to play in pinstripes.
When we got Clemens out in NYC ... he told us he has ZERO doubts the 29-year-old is going to live up to that lofty deal -- saying the ace is just that good.
"We're going to miss him in Houston," Clemens says.