Ferguson believes the Kop are going to need a lot of patience before they get back to where they want to be.
Fergie said: "Anyone going to that club is facing a challenge because they haven't won the League for 20-odd years.
"It is a long time for a club like Liverpool. So for anyone going in there it is a challenge.
"And it's difficult to measure any Liverpool side at the moment with their sides of the past."
The fans and board are backing Rodgers and his long-term vision for the club - and according to Fergie that is what they need to do.
The United boss said: "Patience is a rare commodity in football and if he is getting it, he is very lucky.
"It's terrific if the fans are prepared to be patient as it is going to require patience.
"It is a long road back to what they used to be."