Liverpool hero Graeme Souness suspects Cristiano Ronaldo's age is catching up with him and warned he should no longer expect to start every game for Manchester United.
Ronaldo, 36, has been in brilliant form this season with 10 goals in 14 appearances in all competitions as well as two assists.
However, the Portugal captain has drawn criticism for a lack of effort when out of possession, as he is scarcely seen pressing the opposition defence.
This approach will not be allowed by Ralf Rangnick, who is expected to be unveiled as United interim manager imminently and is renowned for advocating intense, high-tempo football.
The German technician is said to be preparing a radical shake-up at the club's training ground as he looks to get the squad up to speed.
This could involve the installation of a countdown clock which will show players how quickly he expects them to win the ball back and create a goalscoring opportunity.
This will place physical demands on Ronaldo he has not shouldered for many years, arguably since he left Real Madrid to join Juventus back in 2018.
Souness has serious doubts over the five-time Ballon d'Or winner's ability to keep up with the pace of Premier League fixtures and suggested an impact substitute role is more suitable at this stage of his career.
The former Scotland midfielder told the Sunday Times: "I’d have taken Cristiano Ronaldo all day long, but I’d also have had a honest conversation with him: 'You’ll get plenty of game time, but you won’t be starting every game.'
"I still can’t think of a better impact sub, but he’s no longer the player he was - you just can’t be at 36. He may look magnificent when he takes his top off, but you lose power and strength.
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"I’d also have said: 'I’m looking for you to teach these young guys about turning up on time, looking after yourself and training properly, to be the example that takes this club back to greatness.'
"He can still give you all that, but he’s not going to be the go-to man every Saturday, certainly not against the stronger sides. Against Liverpool and Manchester City, he never got a kick because he’s playing with ordinary footballers."
Ronaldo is expected to start up front again as United face Chelsea on Sunday, searching for his first Premier League goal against the Blues.