Jurgen Klopp and Pep Guardiola have criticised the Premier League over the decision to reduce substitutes from five to three after it was initially changed following the Covid-19 break from football.
Following football's return after the coronavirus-enforced hiatus last season, Premier League teams - and most other competitions worldwide - were allowed to make five substitutions as a way of dealing with hectic schedules and lack of preparation.
However, the Premier League decided to return to three substitutions this season despite FIFA's approval to keep the initial change in place until August 2021, with clubs arguing that bigger squads would be favoured by the rule.
Liverpool have picked up a lengthy injury list in the early stages of the campaign, with Virgil van Dijk likely to miss the entire season, while Thiago, Fabinho, Naby Keita, Joel Matip and Alex Oxlade-Chamberlain are also currently on the treatment table.
Klopp feels the Premier League showed a 'lack of leadership' with their decision to cut back on substitutes because of the packed schedules several teams were going to encounter.
"It should be [back on the agenda] but I don’t think it’s possible because of the system," Klopp said.
"It doesn’t help obviously when Chelsea have injuries, and City and Liverpool and United and Tottenham and Arsenal and Leicester, because that is not enough votes for the rest.
"That is the system. I thought it should have been back in in the first place.
"For me it is a lack of leadership just to put the question on the table and say: ‘So what do you want with that?’ It should have been sold – if that’s the right word – differently with more information, showing more of what could happen, by [Premier League chief executive] Richard Masters. We never asked for any advantage.
"None of the top seven clubs asked for any advantage. We just knew, because we knew our schedule, that it would be incredibly difficult. To have the best games at the weekend in the Premier League, it would have helped that as well. I think we should think about it again."
Speaking on Friday, Manchester City boss Guardiola echoed Klopp's thoughts, saying there has been "47 per cent more muscular injuries" this year compared to the same stage of the campaign in 2019-20.
And the Catalan has added his voice to a growing campaign for the Premier League to rethink the decision to only allow three substitutions per game.
"It is nothing to do with certain teams having an advantage," he said. "It is about why we are here - the players. Forget about the advantage; this is to protect all the players.
"When they play every three days, they start to suffer. Why, in all the leagues is it happening, and here we cannot protect the players?
"The statistics speak for themselves. The players are not recovering from the previous game, even the previous season. It makes no sense.
"Who voted for the decisions? Who are they? They have to protect the players. They have to decide. The law is acceptable for FIFA, UEFA."
Manchester City have also been hit by key injuries with Sergio Aguero, Fernandinho, Gabriel Jesus, Benjamin Mendy and Nathan Ake having fitness issues.