Thirty-two teams took part in this year’s World Cup in Russia. Over 700 players from numerous domestic leagues played their part in the events that unfolded during the four-week tournament. Many of the players now have very little rest before they have to start their new domestic campaign.

Some leagues (MLS and Chinese Super League being just two examples) continued playing during the World Cup and while others don’t start until later in the year, the top five European soccer league (Premier League, Serie A, La Liga, Ligue 1 and Bundesliga) all commence in August. This raises the obvious question; what impact does the World Cup have on domestic soccer leagues?

Will players struggle with fatigue?

The main concern for clubs who have players returning from off-season international duty is fatigue. Despite some leagues having a mid-season break (the Premier League the only one of the aforementioned European leagues that doesn’t), the players will have been under increased physical strain over the past six weeks.

Most countries would have started their World Cup preparations less than two weeks after the final game of the domestic season - the majority of them before the very last game of the European soccer season (the Champions League final) had even been played.

Given that players will have been training for three weeks before the tournament commences and then playing as many as seven games in less than four weeks (completely eradicating the usual six week rest period), the adverse effects of fatigue will rightly be a concern.

For the purposes of this article, the data analysed will focus primarily on the Premier League. Below is a breakdown of the top ten Premier League players that exerted themselves the most physically at the 2018 World Cup. 

 These stats for individual players become more interesting when you group them by teams. 

Does team performance change from before and after a World Cup?

This year’s World Cup featured 87 Premier League players. This table shows the number of representatives for each team:

It is to be expected that elite teams have greater representation at major international soccer tournaments thus, will arguably be impacted more by fatigue than other teams at the start of the following season.

In order to try and quantify the impact a tournament like the World Cup has on teams in a domestic season, we can compare the points per game average (PPG) from the final ten games of the season before the tournament against the first ten games of the season after a tournament and split teams by above and below average player representation.

The table below looks at Premier League teams performance in terms of average PPG difference from before and after each of the last five World Cup tournaments.

Obviously there are plenty of caveats that come with this analysis. Average representation is based on the number of players in each international squad and it doesn’t take into account how many minutes they played during the tournament. Additionally, the PPG average is taken from a ten game sample either side of the tournament and the quality of the opponent will not be exactly the same.

Players will have been training for three weeks before the tournament and then playing as many as seven games in less than four weeks, so adverse effects of fatigue will be a concern.

As with any comparison over multiple seasons, it’s important to remember that a lot can happen over the summer break (teams might change manager and recruit new players). It’s also important to consider the change in motivation from the very start of the season when everything is to play for compared to the end when everything might be settled.

Despite the fact that further research would be required before any conclusive results could be found, it is still interesting to note that teams with an above average number of players taking part at a World Cup do appear to suffer a minor drop in performance the following season.

Can the World Cup benefit teams ahead of a domestic campaign?

Although players coming back from a World Cup with fatigue and needing time off during pre-season preparations can be seen as a negative, there are also some potential positives that come with playing throughout the off-season.

The players taking part at the World Cup may be on the verge of “burn out” (physical exhaustion) but continued physical activity will at least maintain fitness levels as opposed to letting them decline during an extended period of rest (although the effects of burn out may arise as the season progresses with little to no rest).

The additional games throughout the World Cup can also help players maintain or improve their form heading into a new domestic campaign. Instead of looking at individual awards such as the Golden Ball (player of the tournament) or Golden Boot (top scorer), taking a more in-depth look at data from the tournament can highlight players who have performed well and may carry good form into the upcoming Premier League season.

There were a few standout performers at the World Cup who play for Premier League teams that could carry that form through to the start of the season. Paul Pogba, Kevin De Bruyne, Eden Hazard, Kieran Trippier, John Stones and Harry Maguire all excelled in chance creation, involvement in attacking process and defensive actions at the 2018 World Cup.

In summary, the effect the World Cup has on Premier League performance is hard to measure. While some research shows a minor dip in performance for teams with an above average number of representatives at the tournament, there are too many caveats and additional external factors that need to be considered.