Mihaylov, son of Bulgarian Football Union president Borislav Mihaylov, failed to gather the ball from a Lucio Vagner's back pass in the 33rd minute of Tuesday's match to concede an own goal.

"I thought he (Mihaylov) was playing very well until that happened," Stoilov said. "We don't have to write off young players just because they are making errors."

"He will continue to be part of the team but now he'll have to be much more responsible, to work much harder and to wait for his revenge."

Werder added two more goals, all in the space of five minutes, through captain Frank Baumann and Torsten Frings.

"It was shocking," said Stoilov. "We conceded the goal and then we were knocked out in the quickest possible way."

"Unfortunately, the big teams waste no time in punishing such mistakes."

The 18-year-old Mihaylov, whose father was keeper for the Bulgarian team that reached the semi-finals at the 1994 World Cup, had only pulled on the gloves because of Georgi Petkov's finger injury.

Mihaylov suffered the wrath of Levski supporters, who started booing him every time he touched the ball, and it was no surprise when he was substituted at halftime.

His place between the posts was filled by 19-year-old Bozhidar Mitrev, making his senior debut.

Levski made a bright enough start at Vasil Levski stadium with Nigerian midfielder Richard Eromoigbe and Croatian-born defender Igor Tomasic coming close to scoring midway through the first half.

"It was a pity as Werder got their opener when we looked like the better side on the field," Stoilov said. "But we are lacking experience and self confidence."