The field for the upcoming Senate special election in Massachusetts has quickly taken shape with three candidates prepared to battle for the Democratic nomination and state Sen. Scott P. Brown the strong favorite for the Republican nod.

But a wild card is lurking: Stephen G. Pagliuca, co-owner of the Boston Celtics, is reported to be eyeing a run as well.

Much of the drama in the special election will play out in the Dec. 8 Democratic primary. That contest likely will determine the state’s next senator, given Massachusetts’ heavily Democratic leanings.

Martha Coakley, the state Attorney General and the only statewide official in the race, is preparing to face off for the Democratic nomination against two Boston-area U.S. House members, Michael E. Capuano and Stephen F. Lynch . Capuano and Lynch have yet to formally launch their bids, but have obtained the nominating papers, the first step toward running.

Pagliuca is seriously considering the race, and would be prepared to self-fund from his own personal fortune, the Boston Globe reported.

Pagliuca has no experience in elected office, but since he doesn’t have to court donors, he would have an instant edge in a race where the compressed time frame makes financial resources all the more valuable.

Also expressing interest in the contest is Alan Khazei, a community activist and co-founder of City Year, a nationwide community service program for young adults. He would have a tough time making headway against the three established Democratic officials and a wealthy self-funder.

All candidates who want to run in the primary must file necessary documents with the office of Massachusetts’ secretary of state by Oct. 20.

After December’s primary, a Jan. 19 special election will fill the seat of the late Sen. Edward M. Kennedy .

Among the three Democrats all but certain to run, Lynch and Capuano begin the race with the advantage of more than $1 million stockpiled in each of their House campaign accounts — funds that the law allows to be converted to Senate campaign accounts.

Coakley is playing catchup on the fund-raising front, though she began with an edge in statewide name recognition, according to a Rasmussen Reports poll conducted Sept. 8.

On Monday, the Coakley campaign unveiled its campaign co-chairs: Barbara Lee , a well-connected advocate for women in politics, and Ralph Martin II, a former district attorney for Suffolk County, which includes Boston. Coakley named state Rep. Katherine Clark and attorney Beth Boland as her campaign finance co-chairwomen.

The campaign also announced that state Senate President Therese Murray will serve as honorary chairwoman of the Finance Committee, signaling key support from the state Democratic Party establishment.