Viktoria Plzen head coach Pavel Vrba says his team were unable to deal with the quality of Manchester City in Tuesday's 3-0 loss.
The Czech league champions failed to contain the big-spending City, who scored three times in 11 second-half minutes through Edin Dzeko, Yaya Toure and Sergio Aguero.
Vrba said his side could not cope against such a strong team, describing them as being far stronger than the teams they are used to facing domestically.
"The quality of opposition is at a different level from our domestic league," Vrba said.
"I am sorry we lost by three goals but we cannot afford to make mistakes like we did when the game was goalless; after conceding, it is so difficult."
Vrba praised goalkeeper Matus Kozacik and rued City defender Pablo Zabaleta blocking a Jan Kovarik shot which would have dragged the hosts back to 1-1.
"We had a decent chance at 1-0 down but we did not take it," Vrba said.
"We were made to pay for this because almost immediately we conceded the second goal.
"This more or less confirmed the result.
"Matus Kozacik was one of our best players; he conceded three goals but prevented three or four others."
Toure's stunning 30-yard effort, which curled into the top corner and left Kozacik helpless, earned applause from Vrba.
"It is never easy to play against good teams like Manchester City. After the opening goal we tried to push forward with more players but they found space in our defence," Vrba said.
"The second goal was a real beauty for everybody who saw it in the stadium; it decided the outcome of the match."