But a spokesman said the Archdiocese of Philadelphia must plan for a visit by Francis whether he shows up or not.
"Our planning all along has assumed the presence of the Holy Father. You have to plan that way," said Kenneth A. Gavin, director of communications for the archdiocese.
"We are certainly hopeful he will attend the event," Gavin said.
The World Meeting of Families is a triennial event that attracts hundreds of thousands of Catholics to the host city.
Gavin noted that a million people attended the Mass celebrated by Pope Benedict XVI at the 2012 event in Milan, Italy.
And that is comparable to Pope John Paul II's visit to Philadelphia in 1979, when more than a million people filled the Benjamin Franklin Parkway to attend Mass.
All 8,500 members of the city's police force were on duty for that historic event.
Francis has emerged as a popular figure showing a common touch and focusing on the poor, and a visit to Philadelphia could generate similar or greater attention.
"The pope has really captured the hearts and minds of people around the world," Gavin said.
He said that the 2015 Meeting of Families, because of its scale, would be costly and fund-raising was underway.
"This is not going to be paid for with archdiocese funds," Gavin said.
Francis, the former archbishop of Buenos Aires, Argentina, was elected in March to lead the church following Benedict's resignation.