Businessman Tom Knox, who finished second to Mayor Nutter in the Democratic primary election four years ago, may be dropping plans for another shot at the city's top office.

Knox declined to comment yesterday, promising an announcement at 10 a.m. today that he predicts will come as a "surprise."

Mayor Nutter is also expected to have a big announcement at that time - an endorsement by former Gov. Ed Rendell.

Rendell, who spoke glowingly about Nutter at a recent fundraiser, is the latest in Nutter's line-up of high-profile endorsements.

With today's news, Nutter appears likely to face no serious competition in the primary or general election.

Knox, who spent $12 million of his personal fortune on the 2007 race, commissioned a poll last week to gauge how he would fare against Nutter in this year's Democratic primary or as an independent in the general election.

Knox, who had said that he would match Nutter dollar for dollar in campaign money if he ran again for mayor, faced trouble with name recognition.

A Franklin & Marshall College/Daily News Poll released two weeks ago showed that 57 percent had not heard of Knox, and another 13 percent were undecided, while 16 percent held a favorable view of him and 11 percent held an unfavorable opinion.

The poll showed Knox trailing Nutter in a general-election rematch 46-28 percent with 26 percent undecided.

The poll also showed that 53 percent thought that Nutter should not be re-elected to a second term.

Knox in September said that Nutter was doing a bad job in his first term and did not deserve a "free pass" to re-election.

Knox flirted first with a primary campaign and then with an independent run in the general election, which would allow him to seek the votes of Republicans and independents along with Democrats unhappy with Nutter. Last week, Knox seemed to shift his focus back to the primary.

So far, former state legislator T. Milton Street, who was released from federal prison last year after serving 26 months for not paying his income taxes, is the only Democrat running against Nutter.

John Featherman, a Republican at odds with his own party in Philadelphia, is the only GOP candidate for mayor so far.

Local GOP leaders have been casting around for another candidate. They met over the weekend with Brett Mandel, who finished third in the 2009 Democratic primary for City Controller, to gauge his interest in running.

Mandel said that he was considering his options, but said that he'd like to shore up some support before running on either ticket.

"I think that if I were to step forward alone in the hopes there would be a groundswell to follow me, this town is not that kind of town," said Mandel.

Former Republican mayoral candidate Sam Katz and state Sen. Anthony Hardy Williams both considered primary challenges against Nutter this year but decided not to run. City Councilman Bill Green flirted with the idea, but is now expected to seek a second term on Council.

Knox in January 2010 dropped his campaign for the Democratic nomination for governor, citing "family reasons" that he declined to discuss in detail.

Knox had said that he planned to spend $10 million of his own money in that race. A campaign-finance report that Knox filed with the state for 2010 shows that he put $101,204 into the campaign while collecting $7,281 in contributions from others.

Knox said when he dropped out of the race for governor that "no less than 50 people" had asked him to consider another run for mayor this year.