They gave away another late lead on Sunday evening against Everton in the Premier League after substitute Marouane Fellaini fouled Idrissa Gueye to concede a penalty in the 88th minute.
Man United currently sit 13 points behind league leaders Chelsea and nine behind fourth-place Manchester City.
Speaking about the side, Neville claims it may take longer than anticipated for Mourinho to turn it around.
“He will be devastated that his team have a softness to them and can’t see games out,” he said.
“That is a manager who has been the best in the last 10 years at seeing games out and getting results and making sure his team don’t concede with five minutes to go.
“At the moment they don’t represent him in terms of what he normally delivers.
“He will defend his team but he will be disappointed. He is four months in at a club where there has been three years of signing players they shouldn’t have done, of some disappointment, lacking confidence, and he has to change it around.
“It’s maybe going to take longer than he originally thought, maybe longer than he normally takes, but I can see certain things happening that are better than last season.”
It hasn’t been a great start for United as their performances have warranted better results than they’ve received, however there is still plenty of time to turn it around.
The clash against Tottenham Hotspur next weekend is a must-win game as Mourinho’s men look to close the gap on the top four and get the campaign back on the right track.