The final match of the year saw them beaten 2-0 by relegated Cardiff City City and Solskjaer is now eyeing an overhaul of the entire squad.
Mourinho told L'Equipe: "Generally, the players can feel a certain erosion, especially when you ask a lot of them.
"When I say that the second season was fantastic, I say it because the potential and the objectives were met.
"I really squeezed, like an orange, to achieve them. When you have a very professional group of players who are ambitious, hard-working and talented, at a structured club, you don't have that erosion.
"When you are almost alone, in that you don't have the support of the club close to you, while certain players go somewhat against the coach, who is the nice guy.
"I don't want to be the nice guy, because the nice guy, after three months, is a puppet and that doesn't end well."