Jose Mourinho’s side slumped to a disappointing 1-1 draw with promoted side Wolverhampton Wanderers at Old Trafford on Saturday.
Manchester United had won their previous three games in all competitions to appear to turn a corner after a slow start to the season.
However, the Red Devils are in eighth spot and eight points behind leaders Liverpool FC after their stalemate with Wolves.
Manchester United have been inconsistent under Mourinho since the Portuguese head coach replaced Louis van Gaal back in May 2016.
Former Liverpool FC captain Souness believes Manchester United will be dangerous if the Red Devils string a series of results together.
“Manchester United are a big football club… when they get on a roll; that makes them dangerous,” Souness told Sky Sports.
“They might not be the best team but if they get a run together, that snowball, come winter, could be a big one. I wouldn’t rule them out.”
Manchester United haven’t won the Premier League title since 2013 when Sir Alex Ferguson was still in charge.
The Red Devils signed Shakhtar Donetsk midfielder Fred, FC Porto defender Diogo Dalot and Stoke City goalkeeper Lee Grant in the 2018 summer transfer window.
Mourinho has won the Europa League and the League Cup during his first season at Old Trafford.
Manchester United finished in second spot in the Premier League table last term to end up 19 points adrift of leaders Manchester City.
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