The chief executive of Simon Property Group Inc said on Thursday a revised plan by management of General Growth Properties Inc to emerge from bankruptcy would not put pressure on his company to sweeten its own $10 billion offer.

Simon CEO David Simon, speaking at a conference at New York University, said that the General Growth proposal lacks certainty despite its new financial backing. Simon, the largest U.S. mall owner, last month offered to buy General Growth, the second-largest, in a plan that had support from many General Growth unsecured creditors.

But General Growth on Monday set forth a competing plan to emerge from bankruptcy, under which William Ackman's Pershing Square Capital Management and fund manager Fairholme Capital Management would invest up to $3.93 billion.

That plan has backing from Canada's Brookfield Asset Management Inc . Pershing Square is General Growth's largest shareholder, and Fairholme its largest debtholder.

General Growth had earlier proposed to split into two companies, in a plan under which Brookfield would have invested roughly $2.63 billion in exchange for a 30 percent stake.

That plan also called for General Growth to sell about $1 billion of assets and raise $3.3 billion of equity.

In a short interview after his conference appearance, Simon said that General Growth's revised plan would not force his company to respond with an improved offer.

I don't feel any pressure on the deal, Simon said. We're going to do what we think is in the best interest of our shareholders.

While General Growth's portfolio of more than 200 malls in 43 states would represent a rare opportunity for Simon Property to cement its leadership in the market, the chief executive was cautious, saying: I don't generally believe that anything is a once-in-a lifetime opportunity.

We'd like to do a deal we think we can make money from, he said.

Simon told the conference that the revised plan retains potential pitfalls for General Growth shareholders.

The first plan had a lot of uncertainty to it, in terms of how it was going to impact shareholders, Simon said at a New York University conference. Their added plan eliminates some uncertainty, but not all of it.

The case is In re: General Growth Properties Inc, U.S. Bankruptcy Court, Southern District of New York, No. 09-11977.

(Reporting by Paritosh Bansal, Ilaina Jonas and Jonathan Stempel, editing by Dave Zimmerman and Gerald E. McCormick)