Manchester United still haven't replaced Roy Keane, according to Alan Smith, who says the Red Devils are "crying out" for a leader in the dressing room.
Keane earned a place in United's hall of fame after a trophy-laden 12-year spell at Old Trafford which saw him emerge as one of the best midfielders in Premier League history.
The ex-Republic of Ireland international won 17 major trophies in Manchester, including seven Premier League titles and the Champions League, racking up 460 appearances for the club in the process.
He eventually ended up leaving the club in November 2005 before undertaking a new challenge at Celtic, and hung up his boots a year later after struggling with injury.
Keane captained United for much of his time at the club, with Gary Neville inhering the armband after his departure as Sir Alex Ferguson ushered in a new era.
The Red Devils continued to enjoy great success across all competitions without a talismanic figure, but the glory days came screeching to a halt when Ferguson stepped down from his post in the Old Trafford dugout in 2013.
By that stage, Neville had already hung up his boots, with Nemanja Vidic subsequently inheriting captaincy duties, and Wayne Rooney, Antonio Valencia and Ashley Young all went on to take on leadership duties before Harry Maguire stepped up to the plate earlier this year.
However, former Red Devils striker Smith claims his old club have never been able to find someone capable of filling Keane's boots, which he sees as one of the main reasons for their struggles during a frustrating traditional period.
"Roy Keane is probably impossible to replace as a player and as a character, especially at Manchester United," Smith told United's official podcast.
"I still don’t think it’s been done now, and it’s been crying out for someone like Roy Keane to be in the dressing room and on the field as Roy was.
"No-one could ever replicate it, so it was [about me] trying to do as good a job in a similar position. It wasn’t like, 'you’re going to be a Roy Keane'. I could never do that job."
Smith went onto dismiss any suggestion that Keane was overrated during his heyday, insisting all of his former team-mates would happily attest to his qualities both on and off the pitch.
"You could ask any player that’s played with him or against him and I’d say 99 per cent of them would all have the same answer for you," he added.
"For me, it’s not just a case of Roy being a leader. That’s so disrespectful to him as a footballer as well. You don’t play for Manchester United and captain them based on just being a leader.
"That’s such an unfair criticism of someone who’s probably been one of the Premier League’s greatest central midfield players."