Ryan Giggs fears Manchester United may have to wait 20 years to win another Premier League title.
United have not won the top-flight since Sir Alex Ferguson retired at the end of the 2012-13 season, with three permanent managers - David Moyes, Louis van Gaal and Jose Mourinho - sacked in the period since.
Liverpool ended their 30-year wait for the title last season after finishing runners-up to Manchester City the previous year, and Giggs fears United could suffer a similar barren run if their north-west rivals continue to improve.
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"It could be 15, 20 years before you know it, especially if (Jurgen) Klopp and (Pep) Guardiola stick around," Giggs told Jamie Carragher, on The Greatest Game podcast.
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"They have got the resources and the players so we have Liverpool to look at where the last time when they won it in 1990 they thought we'll win it again soon.
"Even Klopp took four-and-a-half years for him to win it - it takes a long time. You have to think about what Klopp did.
"He improved the team every season or won a trophy like the Champions League and then you saw the improvement so the pressure was off a little bit.
"Every manager and signing is seen as that he will win us the league and it's not like that."
Manchester City have won the Premier League three times since Ferguson's departure in 2013 but Giggs still sees Liverpool as United's main rivals.
"The best feeling I always had was leaving Anfield after winning even if Liverpool weren't the best side at the time," said Giggs, who won the Premier League title a record 13 times while at United.
"I played for Salford boys and our toughest games were always against Bootle, Liverpool, Kirkby, Sefton.
"As soon as you went down the East Lancs it was a mindset it's going to be a tough game and a test of not just your footballing ability but also your mental strength."
United have struggled for consistency at the start of the season and are currently 15th in the Premier League, having taken seven points from their first five games.
Ole Gunnar Solskjaer's side next face Arsenal at Old Trafford on Sunday, live on Sky Sports Main Event.
Pitch to Post Preview: Jamie Redknapp on Man Utd v Arsenal; plus Liverpool's CB options, and will Everton bounce back?
Jamie Redknapp joins Peter Smith on this week's show to look ahead to Sunday's showdown between Man Utd and Arsenal and says there are more questions than answers at Old Trafford as Ole Gunnar Solskjaer prepares for his 100th game in charge.
Sky Sports News reporter Vinny O'Connor has the latest on Liverpool's injury problems and discusses the young players who could cover at centre-back.
And Sky Sports statistician Matt Cheetham picks out the numbers which explain why Everton's defeat at Southampton could just be a blip, and makes his bold Pitch for what will happen in the Premier League this weekend.