Global footballers’ union FIFPro has reiterated its call for a mandatory rest period of at least four weeks between the final game of one season and the start of pre-season training for the next.

It comes after at least 15 players who participated at the World Cup returned to action in UEFA club competitions less than four weeks after returning from Russia, leaving without a sufficient close season break.

“Players are coming under too much pressure, caught between the needs of their clubs and their own personal well-being,” said the union in a statement.

“While FIFPro understands the financial implications of the UEFA Champions League and UEFA Europa League for clubs, the health of these players is being put at risk because of such a congested match schedule.”

The group stage of the World Cup in Russia, which was officially part of last season, finished on June 28 while the final was played on July 15.

The first round of qualifying for this season’s Champions League began on July 10, meaning that the two seasons in effect overlapped by a few days.

While clubs from smaller leagues are already involved in European qualifiers, big clubs are on lucrative tours abroad.

On Sunday, Manchester United manager Jose Mourinho said his team’s World Cup participants should consider cutting their holidays short to help the depleted team in the opening stages of the Premier League season.

Several players from United’s first-choice starting line-up, including Frenchman Paul Pogba, Belgian Romelu Lukaku and Englishman Jesse Lingard could miss the opening league fixture against Leicester City in less than two weeks’ time.

England defender Phil Jones and forward Marcus Rashford are expected to return early to help prepare for the start of the season.