The Cherries welcome the Red Devils to the Vitality Stadium on Friday night as they attempt to bounce back from a goalless draw at Turf Moor against relegation-threatened Burnley.
That result means it is now four consecutive draws in the league for Iraola’s side, who are seeking to jump above Everton and into eighth in a late European push.
Man Utd aren't impossible to beat
However, with just eight games remaining, Bournemouth must start to pick up three points against the likes of United, who Iraola says aren’t invincible.
"I wouldn't say impossible (to stop United), but very difficult to think that we can get another clean sheet against United. They are scoring goals for fun lately.
"They continue scoring more or less the same amount of goals (under Michael Carrick), but the improvement has been on the other side. They are not conceding goals, but I would say even they are not conceding chances, that is even more difficult."
Iraola is a big fan of Carrick
United interim boss Michael Carrick has now won seven of his opening nine Premier League games and is the favourite to take the job full-time.
Iraola has a lot of admiration for the former midfielder, who has led his side to third as they chase Champions League football.
"Definitely a top player. And I think we are also seeing as a manager everything that he had as a player, how he understood the game. They always say the best managers are midfielders, and he was one of the best.
"I like what he's doing. I don't know him personally, but I also like how he speaks, how he makes everything about the team, about the players, and I think they are doing fantastically."