Law wants United's board to show a similar amount of patience to Sir Alex's successor as they did to the Scot himself in his early days at Old Trafford.
"What do directors need from somebody, have they got to win all the time? At United they were prepared to wait to see what happened," Law told the Daily Star.
"Some people have been winning trophies [and then been sacked] and you think, what do people need?
"The guy at Chelsea [Roberto Di Matteo] won the Champions League, you can't get any higher than that. Can you get any higher than that in club football? No!
"What do people want? I thought that was what you wanted, you wanted a manager to win trophies and play attractive football, which they did."