Mayor Thomas Menino is expected to endorse U.S. Senate candidate Elizabeth Warren at a Friday rally in Roslindale, sources tell the Reporter.

The afternoon rally in Roslindale Square will come after a debate scheduled for Thursday night between Warren and U.S. Sen. Scott Brown. Brown, a Wrentham Republican, and Warren, a Cambridge Democrat, face off on WBZ-TV at 7 p.m. Thursday.

The rally is set for Roslindale Square at 3:30 p.m. on Friday.

Menino, who once declared Brown "unbeatable," appeared to lay some groundwork for an endorsement at a Labor Day breakfast earlier this month.

“I mean, let’s get real about this, guys. You know, he’s a nice guy, but I mean, you’ve got to be with people,” Menino said. “The working people of Massachusetts. That’s what I think about all the time. The people I represent, what do they need? When they’re unemployed, they need unemployment benefits. They need health care. All those issues.”

“I mean, he’s a nice guy but I need a consistency,” he said.

Brown's camp will likely seek to downplay the endorsement, as Warren's campaign has while Brown racked up endorsements from Democrats like state Rep. Chris Fallon of Malden.