Neil Lennon believes domestic pressure has prevented Celtic from improving in Europe over recent seasons.
The Scottish champions have not won a knockout game since defeating Barcelona in 2004 in the UEFA Cup.
And Lennon feels the Hoops could do more in Europe if they were able to take their foot off the gas domestically.
As quoted in Football Scotland, he said: "There isn’t a glass ceiling for Celtic when it comes to Europe. I remember saying the same thing in my time as manager when we lost to Juventus in the knockout round.
"The club will burst past that at some point and I admit I had some disappointments when I was in charge. We really should have gone through against FC Copenhagen in 2020, for example.
"Part of the problem is Celtic are always going flat out in the Premiership and the domestic cups. Teams like Sevilla know they won’t win La Liga, so they rest key players in the league and prioritise the Euro competitions.
"That’s why they’ve been able to win the UEFA Cup and Europa League seven times. Real Madrid have been European champions a record 14 times, but they’ve only won the Spanish title four times in the last 15 years because it’s not as important to them.
"A lot of clubs will sacrifice their league positions for European runs, but Celtic can’t afford to do that.”
