Pitta was carted off the field after colliding with safety James Ihedigbo in the back of the end zone vying for a pass from Joe Flacco. The receiver lay prone for several minutes before the cart arrived.
The Ravens begin defense of their Super Bowl title on Sept. 5 in Denver. Pitta will at least miss that game, Harbaugh said, but the severity of the injury could keep the tight end out for much longer than that.
The Ravens re-tweeted a story by ESPN in which a league source said Pitta would miss the entire season.
Baltimore general manager Ozzie Newsome did not immediately answer a text message from The Associated Press seeking information on Pitta's status.
After practice, a somber Harbaugh said, "Dennis has a dislocated hip. We'll have to take a look at that and see exactly what it is. It's a serious injury. He is going to be out for a while. He will not be in the Denver game and we'll just have to play it from there to see how long it goes."
Late Saturday night, a Ravens official said the club had no update from doctors or Pitta. He said the team website regularly re-tweets stories and updates from various news agencies.
Pitta was preparing for his fourth season with Baltimore.
In the playoffs, Pitta had 14 catches for 163 yards and three scores.
With Pitta gone, the Ravens are without their two of their most productive receivers last year. Pitta's 61 catches were tied for second with Ray Rice behind Anquan Boldin, who was traded to San Francisco during the offseason.
"Obviously, he was a very, very productive guy for us," Ravens offensive coordinator Jim Caldwell said of Pitta. "He made a lot of big plays last year. We'll see what happens. But somebody is going to have to step up. We do have some capable guys all across the flanks. We do have some weapons. We're just going to have to have some guys make some plays for us."
In his first three NFL seasons, Pitta has 102 receptions for 1,075 yards and 10 touchdowns over 43 regular-season games.