West Brom boss rues lack of patience in modern game
The Baggies play City at The Hawthorns on Sunday knowing that a win would take them above their wealthy visitors, as well as heap more pressure on Mancini.
"There doesn't seem to be a lot of patience in the last couple of years," he said.
"It makes it difficult. You lose a couple of games and you're under enormous pressure.
"Once upon a time you got a bit more time to work with players and build a team, so I guess it's just the way things are going at the moment.
"It's about short-term results rather than long-term targets."
Di Matteo admits the pressure on Mancini is not unique, as all bosses are expected to get results.
He said: "I think it's part of our job. If you lose a couple of games you're going to be put under pressure. That happens to everyone.
"It's not something that happens at just one club. It's the nature of our profession.
"Every club has its level of expectation. They are expecting as much from him as any other chairman expects from his manager.
"If I was bottom of the table you can imagine what kind of pressure I would be under. It just comes with the size of the club and the budget they have.
"It's normal that there's pressure on big clubs because they invest and they expect, but my chairman expects results from me."