Ole Gunnar Solskjaer has bemoaned the decision by Premier League clubs to vote against using five substitutes this season.
The rule was brought in when the 2019/20 season restarted in June after a three-month hiatus because of the coronavirus pandemic.
But the top-flight has reverted to three substitutions, something Solskjaer believes has contributed to the number of injuries this campaign in a congested calendar.
Asked whether he was in favour of five substitutes, Solskjaer said: "One-hundred per cent. I don't understand and I cannot believe the vote went against because we have to look after the players.
"We have to think about the players. This season is the most demanding season of all.
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"I can see the point why clubs voted against but if you take a step back and think about these professional footballers and their mental and physical health the only sensible solution would have been to give us the opportunity to rest a few more.
"We have already seen a lot of injuries in the Premier League. I would have liked to have five subs."
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Solskjaer has faced questions in recent weeks over a lack of game time provided to summer arrival Donny van de Beek but the Norwegian is adamant the club's squad depth will prove a benefit rather than a hindrance this season.
"At the moment we are looking like a Man Utd squad," he said.
"I have got opportunities, competition for places. Any successful team in the modern era of football has had that option to rest players [and] to rotate.
"That is probably the only way you can last in this most intense league in the world, [being] also involved in the Champions League and you want to go for the trophies."
United are unbeaten in their last four matches and Solskjaer is encouraged by the response of his players since the "brutal" 6-1 defeat against Tottenham earlier this month.
"We've tweaked a couple of things, got players fit and I think the manner of the defeat wasn't something we should ever have to be confronted with again," he said.
"Then again things happen in football these days and the response has been fantastic, and that's what I'm concerned about, because we wanted to finish that off as soon as we could and move forward."
Solskjaer's tenure in charge at Manchester United
Across Ole Gunnar Solskjaer's previous 99 games in charge, Manchester United have won 55, drawn 21 and lost 23.
Solskjaer will face Arsenal on Sunday in his 100th game in charge of United and he is expecting a more open title race this season.
During his playing career the Gunners were a direct rival in the league before Chelsea also emerged as title challengers, but Solskjaer believes the start of this season has underlined the improvement across the board within the top-flight.
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"I think football has developed and so many clubs have developed strength in depth and the ability to challenge for the trophies," he said.
"Even though the last two seasons you had two teams (Manchester City and Liverpool) running away with it, I think this season a lot of us just underneath them would hope to put up a challenge. Back then it was us or Arsenal, and then Chelsea came through.
"Now it's more exciting for me and the fans that it's not one of these two. Anything can happen this season with what's happening around the world and we're just taking one game at a time."
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Pitch to Post Preview: Jamie Redknapp on Man Utd vs 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.