Attorney Gloria Allred announced Monday evening that she and her client, Irene McCormack Jackson, spent the day in mediation at a downtown office building, where Filner was spotted by a TV crew entering earlier in the day.
Allred wouldn't say whether Filner's resignation was discussed nor whether the mayor was present. She said the mediator, former federal judge J. Lawrence Irving, asked that no one make comments while talks continued.
Filner is facing a recall effort prompted by the cascade of sexual harassment allegations that also led the entire City Council and many leading Democrats to call for him to step down, including U.S. House Minority Leader Nancy Pelosi and U.S. Sen. Barbara Boxer.
Filner has vowed to remain the leader of the nation's eighth-largest city and said he would return to work Monday after completing an intensive two-week therapy program. His lawyers said he also spent one week in outpatient counseling.
Before going into therapy, Filner vowed when he returned that his "focus will be on making sure that I am doing right by the city in terms of being the best mayor I can be."
But he wasn't seen Monday at City Hall, where a few dozen Filner supporters rallied outside, engaging in heated arguments with opponents.
"The mayor coming back to City Hall is the wrong message," Councilman Kevin Faulconer said Monday. "There is no way that he is able to move any type of agenda forward."
Faulconer said the mayor needs to "quit dragging the city of San Diego through this. He needs to resign. He needs to go get the help that he clearly and desperately needs."
Faulconer was later seen entering the building where Filner was spotted by KFMB-TV in San Diego. The councilman referred questions to the city attorney's office, which declined to comment.
Allred said she and her client would not be returning Tuesday.
Steve Erie, a political science professor at the University of California, San Diego, said Filner's resignation must be part of the settlement discussions. Filner would benefit from waiting it out, Erie said, since his pension would spike after serving a year, which would be in December. He also may be trying to shed financial responsibility for the lawsuit.
"As long as he doesn't resign, he has leverage," Erie said. "So stay tuned."
McCormack was the first to go public with harassment allegations. Since then, his accusers have included a university dean to a retired Navy rear admiral. Some contend he cornered, groped and forcibly kissed them.
Filner, 70, served 10 terms in Congress before being elected mayor in November. The feisty liberal has long had a reputation for berating employees and has been dogged by rumors of inappropriate behavior toward women. But nothing in his past approaches what has surfaced in the past six weeks.
Questions also have risen over his spending and a trip to Paris. At least four agencies are investigating Filner: the city attorney's office, the state attorney general's office, the Sheriff's Department and the U.S. attorney.
City Council President Todd Gloria said the city's daily operations have been running fine without Filner but the city needs a leader to set policy.
"Those of us who have called on the mayor to resign know he is not being effective at this time," Gloria said.
Filner's spokeswoman Lena Lewis and lawyer James Payne did not respond to calls.
If Filner should resign, Gloria would step in as acting mayor.
The recall petition drive started Sunday. Organizers must collect 101,597 signatures of registered San Diego voters by Sept. 26. If the petition has fewer than that, the recall campaign will have 30 more days to circulate a supplemental petition to gather additional valid signatures.
If enough signatures are validated by the city clerk, the petition will be presented to the City Council, which must schedule an election within 60 to 90 days.