House Speaker John A. Boehner (R-Ohio) on Tuesday said he was not certain what might happen if congressional leaders and the White House don’t come up with a debt-limit agreement by an Aug. 2 deadline.

“I don’t know,” Boehner said after a lengthy pause when asked by Fox News Channel’s Bret Baier what might happen if the ongoing debt-limit negotiations with the White House fail to produce a deal.

“This is how serious this is,” he continued. “I think the president understands how serious this is, and so do my colleagues. I don’t think we can miss this opportunity. It’s important for us to do this.”

He later added that “I don’t think anybody in the world believes that the United States is going to default on our debt,” but that missing Aug. 2 “could spook the market, and you could have a real catastrophe.”

“Nobody wants that to happen,” Boehner said.

Boehner’s comments came hours after Senate Minority Leader Mitch McConnell (R-Ky.) unveiled a “back-up plan” earlier Tuesday in case the debt-limit negotiations falter. The proposal — which would shift the political burden of raising the debt limit to President Obama instead of congressional Republicans — took many House members by surprise, and several expressed skepticism about it at votes Tuesday evening.

“If it gives the president the authority to raise the debt limit without congressional approval, I’m opposed to it,” said Rep. Tom Price (R-Ga.), who as chairman of the Republican Policy Committee is the fifth-ranking House Republican. “I haven’t seen it. ... I don’t see how we could support that.”

Boehner said during Tuesday’s interview with Baier that he supported the general idea of a back-up plan and thought McConnell had “done good work.”

“I understand Mitch’s frustration because we are all frustrated by where we are,” Boehner said. “Mitch pointed out with his idea is if we can’t get there, none of us believe we ought to default on the full faith and credit of the United States government.”

While Republicans control the lower chamber, many rank-and-file GOP House members have already said they will oppose any effort to raise the debt ceiling, meaning that Boehner will likely need the support of several dozen Democrats in order to pass a deal.

That was the case in April, when 59 House Republicans voted against the fiscal year 2011 funding deal negotiated by congressional leaders and the White House.

Asked whether he believed it was possible that a similar number of Republicans might defect on the debt-limit vote, Boehner responded, “I would agree with that statement.”

“There are a lot of members who just don’t believe that raising the debt ceiling under any circumstances makes sense for them,” he said.