One argument is that profit and sustainability rules are holding back English sides.
At present, clubs cannot report losses of more than £105m over a three-year period – meaning clubs such as Newcastle, who were in the Champions League this season, cannot spend the money they have.
Everton and Nottingham Forest have both been deducted points for breaching the rules.
Speaking after Wednesday’s Champions League games, BBC football correspondent John Murray said: “They [Premier League teams] have become the traditional powerbase so this is a shock to the system.
“We’ve been hearing for years that part of the reason we have profit and sustainability and financial fair play is because of the power of so many Premier League teams. They have attempted to clip their wings. Has that played a part this season and meaning they’re not as strong as they might have been? Probably.”
Spanish football journalist Guillem Balague said it is too early to read anything into this.
“The teams are tired or not sharp at this stage of the season,” he said. “The Premier League is so demanding. To come up with a conclusion give me five years. This could be a consequence of a bunch of things.
“If it happens for five years maybe there’s a problem somewhere. I don’t think you’ll get that. I think you’ll get the dominance of English teams that we’ve already seen will continue next season. This is an accident I think.”