"The bottom line is I think that he [Obama] is a fighter. I think that he will come to the conclusion that he let Romney get away with a little too much, trying to be very presidential, and I don't think you'll see the same thing in this next debate," Schumer said on MSNBC's "Andrea Mitchell Reports."
"That challenger goes up for a little while in the polls, but then tends to go down," said Schumer.
Obama took a dip in the polls after a debate performance last week that many, including some supporters, saw as subdued.
Post-debate surveys show Romney taking the lead, with a Pew Research poll released Monday showing the GOP nominee ahead 49 percent to 45 percent among likely voters. A Gallup poll released Tuesday showed Romney with a 2-point advantage over the president.
The next head-to-head match-up between Obama and Romney is slated for Oct. 16 at Hofstra University in Hempstead, N.Y., and will include foreign and domestic policy questions from voters in a town-hall format.
Schumer also offered advice to his former Senate colleague, Vice President Biden, in his upcoming debate with Romney running mate Rep. Paul Ryan (R-Wis.) Thursday, Oct. 11 in Danville, Ky.
The New York lawmaker said he would tell the vice president to "be yourself, Joe."
"Joe Biden is a genuine person, a down-to-earth person. I've known him for thirty years," said Schumer. "He's got great political instincts, and I think one of the things that happens in these debates, if you overthink it, get over-handled, and you're not yourself, the public can see that. So I would tell Joseph Biden: 'Be yourself, you're very good at this,' " he said.
Schumer also discussed his push for an overhaul of the tax code that breaks with precedent and raises rates on the wealthy.
"[S]omehow people have bought on to this theory that as part of deficit reduction we ought to lower the top rate on the highest income people. You lose a ton of revenue there and you can't make it up unless you really squeeze the middle class," he said.
He called for using revenue from closing loopholes to lower the federal deficit, rather than reducing the tax rate for top income earners.
Read more on Schumer's tax proposal on The Hill's On The Monday blog.