Mourinho was sent to the stands after kicking a water bottle during his side’s 1-1 draw to West Ham on Sunday and has been subsequently charged by the Football Association with “improper conduct” for the second time this season.
Souness has not been impressed by the Portuguese’s behaviour and believes the coach is acting like an amateur.
“He’s a vastly experienced manager but some of his antics suggest he is just a new guy starting off in the game,” he said.
“He won’t be enjoying that being said about him. But in terms of football, I think he is being let down by his players.
“That group of players should have more points in the bag than they have so far."
The former Liverpool player added that Mourinho does not yet know his strongest XI but that his players are failing to help the manager’s cause.
“I thought Man United would be flying, but we’re nearly in December and I don’t think Jose knows his strongest XI,” Souness said. “He’s still scratching for that and not getting results.
“What you are looking for as a manager is players to say, ‘you can’t leave me out’.
“I don’t think Man United players are making that statement.
“They have a lot to choose from so are making changes to try and get a result and then you find the ones you are playing are not any better than the ones from the previous week.
United’s recent run of results certainly suggest that the side have struggled to find their form as a team. Sunday’s game against West Ham marked the side’s fourth consecutive draw at Old Trafford and leaves United 11 points adrift of league leaders Chelsea.
But despite the Blues’ impressive run of results, Souness admitted the title race remains wide open.
With just three points currently separating the top four of Chelsea, Liverpool, Manchester City and Arsenal, the 63-year-old conceded: “It’s more like the Premier League this year.
“The usual suspects are there and it is impossible to predict the outcome.”