The market is contending with several scary scenarios that have put a serious crimp in the stock rally. The idea that the U.S. could carry out military strikes on Syria, combined with renewed pessimism about the debt ceiling debate, led the S&P 500 to drop over 1.5 percent Tuesday.
But Krishna Memani, OppenheimerFunds chief investment officer of fixed income, said such concerns are little more than red herrings. The real problem, he cautions, is slow economic growth.
Concerns about the debt ceiling came to the fore on Tuesday, when Treasury Secretary Jack Lew wrote a letter to congressional leaders saying that the U.S. will hit it in mid-October. When that happens, the government will not be able to issue more debt without authorization from Congress. And given how divisive that body has become, even another short-term authorization to keep the government functioning is not counted as a sure thing.
Lew's comments on "Squawk Box" didn't indicate that a compromise is imminent.
"We're not going to be negotiating over the debt limit," Lew said. "Congress has already authorized funding, committed us to make expenditures. … The only question is, will we pay the bills that the United States has incurred?"
(Read more: Lew: Obama not negotiating over debt limit)
Meanwhile, many Republicans have said that they would not vote for a bill avoiding a shutdown without the (unlikely) concession of defunding Obamacare. As Sen. Ted Cruz (R-Tex.) recently put it, "If you have an impasse, one side or the other has to blink. How do we win this fight? Don't blink."
Memani downplays the White House and Republican rhetoric.
"If they don't compromise, then that clearly is bad for the economy," the fund manager said. "But it don't think that's really a base-case scenario, because we have seen this movie several times before."
Indeed, while the fiscal cliff negotiations were exceedingly ugly, Congress did manage to pass an 11th hour compromise.
"There's a lot of posturing that takes place, but at the end of the day, we find a way of resolving the issue," said Memani. "And this time will be no different."
Similarly, he said, the Syrian situation will not be "a driver of pricing." Many market participants make the point that that situation introduces short-term uncertainty more than a major headwind.
(Read more: Syria is just the latest of the market's troubles)
In his view, the market's biggest problem is slow growth—and that is the reason he sees Treasury yields rising.
"I think rates are going to rally, but they are going to rally on the back of a weakening economy, and economy that's not growing very fast, rather than the debt ceiling or Syria," said Memani, who manages $80 billion in assets.
So what will that ultimately mean for Treasury yields this year?
"I think that by the end of the year, rates are probably going to be closer to 2 percent than that 2.75 or 2.8 that we are at currently. And that view is predicated on the fact that the economic growth that we're looking for in the Fed's forecasts is probably a bit overstated," Memani said. "And if we have 2 percent growth for the foreseeable future, I think it's probably closer to 2 percent for 10-year Treasurys than 3 percent or 3.5 percent."
(Read more: The 3 reasons everyone is dead wrong about bonds)
Investors looking for a reason to be bearish, then, perhaps should set the nightmare scenarios aside. According to this big-time fund manager, they need look no further than the regular old U.S. economy.
—By CNBC's Alex Rosenberg. Follow him on Twitter @CNBCAlex.
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