They said today that Khaled Ali will announce his candidacy on Monday.
The politicians are close to Ali and have been directly involved in months-long consultations between him and leaders of secular democratic parties on fielding a joint candidate against el-Sissi.
They spoke to The Associated Press on condition of anonymity because Ali has not yet made an official announcement.
El-Sissi, who led the 2013 ouster of an Islamist president, has yet to formally announce he will run for a second, four-year term, although his candidacy is a virtual foregone conclusion and is almost assured of winning.