The Red Devils face Chelsea in the FA Cup final this afternoon (5:15pm kick-off).
Mourinho is looking to win his third major trophy during his time at United, with the Special One also lifting the Europa League and the EFL Cup last season.
And Gudjohnsen, who played under Mourinho during his time at Chelsea, has hit out at United, claiming his former boss is too defensive.
“They haven’t excited us this year, probably this year a bit more than last season,” Gudjohnsen told BBC Sport.
“I thought they were boring last season.
“This year at times they’ve played some better football but there’s still something lacking.
“We all have the sense that Mourinho goes into games with a defensive mind and doesn’t play the attacking football that this team can.”
Speaking ahead of the FA Cup final, Mourinho revealed another trophy would make this season a successful one for United.
“Of course it makes a difference, but it’s one thing to make a difference and the other is to consider the season good or bad because of one match,” he said.
“I analyse the work I do, the effort I put in, and everything we all did at the club. I’m not going to analyse them because of one – of course very important – match.”
Mourinho will start David De Gea against Chelsea this afternoon, while Romelu Lukaku faces a late fitness test to decide if he can face his old side at Wembley.