NEW YORK (AP) — Mistimed hedging calls and asset sales will weigh on Chesapeake Energy, Sterne Agee said Tuesday, as it downgrade the shares of one of the nation's biggest natural gas drillers.

Analyst Tim Rezvan said company shares have risen about 33 percent this year, outpacing the 16 percent increase for the sector as a whole. But guidance for this year could be at risk, given the need to fund operations through asset sales, he said.

The company has already hedged a substantial portion of this year's production at too low a price, Rezvan said, and it needs to sell off another $3 billion to $4 billion in assets to fund its operations this year.

The Oklahoma City company has sold off billions in assets to pay off debt incurred as it rushed to buy land and other assets, turning itself into a behemoth just before the natural gas boom took off. The ensuing natural gas blitz pushed prices down to 10-year lows, hitting companies hard that had invested so heavily.

The company announced earlier this year that Aubrey McClendon, who founded the company and aggressively built it into a market leader, would retire. The last several years of McClendon's tenure were marred by questions about loans from a company that Chesapeake was doing business with.

Chesapeake has already hedged 45 percent of its 2013 natural gas production at $3.63 per thousand cubic feet, Based on his calculations, natural gas prices could reach about $3.85 per thousand cubic feet this year, meaning the company will not fully benefit from rebounding prices, Rezvan said.

Chesapeake's spending plans hinge on more asset sales and Rezvan believes that the company still needs to find more than $3 billion in funding. If those sales don't happen, the company's 2013 guidance could be at risk, he said.

Sterne Agee downgraded shares to "underperform."

Shares fell 27 cents to $21.90 in premarket trading.