"Like I've already told a bunch of guys on the team, we've got Pittsburgh; that's a must-win. We've got a bunch of must-wins, but the San Francisco game is going to be a must, must-win," Harbaugh said with a laugh. "There's no doubt the motivation for that one is going to be there."
John Harbaugh signed a three-year extension last month that will keep him under contract with the Ravens through 2014. He's led Baltimore to the playoffs in each of his three seasons after replacing Brian Billick as coach in January 2008. Baltimore is 32-16 in the regular season under Harbaugh and 4-3 in the playoffs.
John suggested his brother Jim would have the 49ers playing hard next season, his first in San Francisco.
"One thing about that football out (in San Francisco) I think you'll find, it's going to be competitive, it's going to be exciting," John said. "You know, Jim's personality will blend well with the players they have there, and I'll be rooting for him 15 games next year."
The Associated Press contributed to this report.