Singletary, 48, has spent the last two seasons as San Francisco's assistant head coach/defense and in 2003 and '04 he served as inside linebackers coach for Baltimore.
The pending interview further puts the Cowboys in compliance with the "Rooney Rule," which states a team must interview at least one minority for a head coaching vacancy. According to the NFL, the Bowles' interview had satisfied the rule.
He appears to remain the lead candidate.
San Diego Chargers defensive coordinator Wade Phillips, who interviewed with the Cowboys on Friday, said Monday afternoon he has not heard back from the team.