Arsenal boss Arsene Wenger believes the intensity of the Premier League hurts English clubs' chances to compete in the Champions League.
The Gunners suffered a shock defeat to Dinamo Zagreb in their Group F opener and resume their campaign against Olympiacos on Tuesday.
English club have struggled to make it to the latter stages of Europe's premier competition in recent seasons and Wenger believes the frantic nature of the Premier League is to blame.
"These teams dominate their leagues," Wenger told reporters at his pre-match press conference.
"Olympiacos won comfortably on Saturday, they were safe after 20 minutes, when we were in a high-intensity game at Leicester.
"Mentally you cannot ease off before a Champions League game, as some others can.
"For example Dinamo Zagreb played on Saturday and they took three players off at half-time. I cannot do that at Leicester.
"For sure the Premier League is demanding and consuming energy wise – mentally more than physically."