Coventry's Iain Dowie and Plymouth chief Ian Holloway are also believed to have been shortlisted.
"It is difficult to get a good manager as they are all at clubs," said Mandaric.
"But we are approaching clubs confidentially. I will not do it publicly as I do not want to destabilise those clubs because that is not fair."
Peter Reid, Joe Royle and Jean Tigana have also been linked with the post - which became available when Gary Megson quit the club just six weeks after being installed.
And Mandaric hopes to have his new man in charge by the end of the international break.
"We need to sort it out quickly - over the next week or 10 days during this break," Mandaric added.
"We need a manager to come in and sort us out and get us on a winning streak and that must happen immediately.
"I will keep working on the shortlist to get someone on board who can do that."