Premier League injuries: Why are so many players getting injuries this season?

Arsenal's Bukayo Saka is helped off with an injury against Leeds United on Sunday

One topic is dominating the thoughts of Premier League managers this season - injuries.

Liverpool boss Jurgen Klopp once again questioned the fixture schedule after his side's 3-0 win over Leicester - and with a condensed season, players do appear to be sustaining injuries at a higher rate this campaign.

According to Premier Injuries, which compiles a database of injuries in the top flight, there have been 133 muscle injuries in total over the first nine matchdays of this Premier League season, a 23% increase compared to the same period last year.

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Who are the key players out?

Arsenal: Defensive midfielder Thomas Partey is out with a thigh injury. Left-back Bukayo Saka sustained a knee injury and winger Willian suffered a muscular injury against Leeds.

Aston Villa: Midfielder Ross Barkley was substituted with a hamstring injury just five minutes into defeat by Brighton on 21 November.

Brighton: Midfielder Adam Lallana was replaced at half-time against Aston Villa on 21 November because of a groin injury.

Burnley: Winger Robbie Brady sustained a hamstring injury against Crystal Palace on 22 November.

Chelsea: Forward Christian Pulisic has started only two Premier League matches this season because of a hamstring injury.

Everton: Captain Seamus Coleman is out following a recurrence of a previous hamstring injury.

Leicester: Currently without defenders Caglar Soyuncu and Ricardo and midfielders Wilfred Ndidi and Daniel Amartey.

Liverpool: Defenders Virgil van Dijk and Joe Gomez are expected to miss a significant part of this season after both had surgery on knee injuries. England left-back Trent Alexander-Arnold is also out with a calf injury.

Midfielders Naby Keita and Xherdan Shaqiri are out with muscle injuries, while Jordan Henderson and Thiago Alcantara are yet to return.

Manchester City: Striker Sergio Aguero is still not fully match fit. Defender Nathan Ake sustained a hamstring injury in the Netherlands' 1-1 friendly draw with Spain, while left-back Benjamin Mendy is still out with a muscle injury.

Manchester United: Defender Luke Shaw has been ruled out for a month with a hamstring injury.

Newcastle: Striker Callum Wilson is out with a hamstring injury, while defender Jamaal Lascalles injured his thigh in defeat by Chelsea on 21 November.

Southampton: Striker Danny Ings, who has scored five goals in seven games so far, will be out for up to six weeks with a knee injury.

Tottenham: Defender Toby Alderweireld is facing a spell out after appearing to injur his groin in victory over Manchester City on 21 November.

West Ham: Forward Michail Antonio is out with a hamstring injury.

Why are there more injuries this season?

The lack of a normal pre-season this year and a packed fixtures schedule are both factors behind the rise in injuries, says former Arsenal and England physio Gary Lewin.

He told BBC Radio 5 Live: "If you're not fully recovered from your previous game then fatigue will set in and muscle injuries will go up, because if you have tired muscles and you load them again, they are going to break."

There were seven weeks between the 2019-20 Premier League season ending and the 2020-21 campaign starting, compared to 12 as originally planned, because of the coronavirus pandemic.

Clubs involved in European competition had fixtures during that time, while there were also international matches.

There will be no winter break this year and the campaign will be five weeks shorter than a standard season because of the late end to 2019-20 and the rescheduled European Championship, starting on 11 June.

It means there are more midweek fixtures this year and weekend games are spread across Friday to Monday because of broadcast selections.

Fatigue and fixture congestion does not account for every absence, with some players injured in challenges and others forced to miss games after testing positive for Covid-19.

What have managers said?

Liverpool boss Jurgen Klopp has urged broadcasters to talk to each other about the football schedule, saying otherwise his side will struggle to finish the season with 11 players.

Manchester City manager Pep Guardiola and Manchester United counterpart Ole Gunnar Solskjaer have also expressed frustration with the fixture scheduling.

Klopp and Guardiola have led calls to reintroduce five substitutes in a bid to curb injuries, citing a study that shows a rise in muscles injuries this season, with Solskjaer and Chelsea's Frank Lampard also in support.

West Ham boss David Moyes said he had changed his mind after initially backing the return to three substitutes.

However, Aston Villa manager Dean Smith believes the Premier League should stick to allowing three substitutes only.

Will five subs return?

English Football League clubs will be allowed to use five substitutes per game for the rest of the season after the EFL board agreed to the change following consultation with the 72 teams.

However, Premier League chief executive Richard Masters said earlier this month a return to five substitutes per team in matches is unlikely.

He said clubs have twice rejected the move, with the proposal needing a minimum of 14 clubs to support it for the rule to be changed.

BBC Sport understands that, on the last occasion, 11 clubs were in favour, while other members feel the five substitutes allowance unfairly benefits major clubs.

The rule was brought in when the 2019-20 season restarted in June to protect player welfare and world governing body Fifa allowed its continued use this season.

The Premier League is the only major competition in Europe to return to three subs.

Would they actually use five subs?

Only five sides - Arsenal, Manchester United, Newcastle, Spurs and West Brom - have used all three of their available substitutes in every Premier League game they have played so far this season.

Burnley have not used all three substitutes in any of their eight matches to date.

Teams are still allowed to use up to five substitutes in European competition.

In the Champions League this season, Liverpool have used five substitutes in all three of their group games, while Chelsea, Manchester City and Manchester United have used all five in two matches.

Chelsea used four substitutes against Sevilla, while City and United used three against Porto and Paris St-Germain respectively.

In the Europa League, Spurs have used five substitutes in all three games, Leicester have used all five in two matches and four in one and Arsenal have twice used four substitutes and all five in one match.

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