Former Manchester United captain Robson has left Bramall Lane after turning down a director of football position, with Kevin Blackwell taking the reins.
Old Trafford boss Ferguson said: "The problem for him at Sheffield United was that the previous manager supported the club and did a good job.
"It was a very difficult role for him to take - no-one has any patience today."
Ferguson added: "Bryan is one of the good guys in the game. He did a great job at Middlesbrough and West Brom.
"Sometimes when you lose your job, you lose faith in yourself but he is a strong person."