Now with Shangdong Luneng, Fellaini slammed United's sack culture.
He told the Daily Mail: "They brought in [David] Moyes, they didn't give him time. They brought in [Louis] Van Gaal, they gave him two years and we started to do some things, he won the cup, but after that they sacked the manager because they want to win quickly.
"For me the club were too quick to sack Jose [Mourinho] because a manager like that comes and he needs a lot of players to do his own philosophy.
"He wanted to build his team but after two years and a half they decided to sack him because the results were not there.
"That's the problem, they have to find a solution together. A manager like Van Gaal, tactically is very strong and a lot of experience and they sacked him.
"They brought in one of the best managers in the world in Jose Mourinho, he wanted to build a team and they sacked him.
"It's not easy to build a team in that time, you need more than two years.
"I don't know what they will do with Ole. Mourinho, for the first season, he did amazingly, he improved the team, won things.
"Okay the second season, was a bit more difficult, but he tried and did his best to help the team."