Time is running out to get insurers into Obamacare and stave off a dearth of competition in one-third of U.S. counties.

The reason for the lack of competition is pullouts by major insurers such as Aetna and UnitedHealth. An analysis from the consulting firm Avalere Health predicted that a third of counties would only have one Obamacare competitor after the insurers leave the exchanges.

For example, Aetna's recent decision to leave 70 percent of the Obamacare markets it offers plans in has left Pinal County in Arizona without any Obamacare plan issuer.

The Obama administration fiercely pushed back against the Avalere study, saying that it was incomplete and premature because new insurers could enter the market before open enrollment starts Nov. 1.

"A number of steps remain before the full picture of marketplace competition and prices are known," the administration said last week.

However, the insurance industry said it is doubtful that new insurers will step in at the last minute.

"Plans are in the process of finalizing their rates now with both states and the exchanges," said Clare Krusing, spokeswoman for Americans Health Insurance Plans, the industry's top lobbying group. "While we can't speak for any individual insurer or company and their business decisions, it's unlikely at this point that any new plans [those not already participating in a state market] would be able to compete in 2017."

It is past the deadline for filing requested rates, which must be finalized by state insurance regulators.

However, state or federal regulators could waive the deadline if an insurer showed interest, said Katherine Hempstead, senior adviser for the nonpartisan Robert Wood Johnson Foundation.

"I think more than new carriers we may see some carriers taking on new rating areas in states where there is thin coverage, although that might come with revised rates," she added. "I think there is definitely still an opportunity to get existing carriers to cover more territory within a state."

The deadline to file a qualified health plan with the federal government that will then be offered on the exchange is Sept. 23.

Some state regulators are exploring new ideas to entice more Obamacare issuers to offer plans. Minnesota's Obamacare exchange MNsure asked the public for comment on what state laws or rules can be waived to offer new coverage to residents outside of the Twin Cities area, according to the Minneapolis Star Tribune.

The Tribune noted that the timing of the request, which is three months before open enrollment, suggests concerns about a lack of competition in Obamacare.

The administration has said that entry and exit is a normal part of any market, especially one that is still developing. Insurers will still want to participate on the market because it is an "important growth opportunity for them," the administration has said.

Some insurers such as Aetna and UnitedHealth have opted to do the opposite, while others such as Anthem and Cigna remain committed.

Meanwhile, higher premiums are likely in store for Obamacare customers. Tennessee regulators announced Tuesday that they had approved increases of as much as 60 percent in 2017.

The price hikes and others around the country are due partly to a market correction as insurers largely underpriced their plans when Obamacare exchanges went online in 2014.