Answer
The correct answer is 2004. Valdez debuted in the UEFA Champions League with FC Schalke 04 in the 2004-05 season. He made his debut on September 14, 2004, in a group stage match against AEK Athens. He came on as a substitute in the 68th minute and scored the winning goal in the 89th minute. Valdez played in six more Champions League matches that season, helping Schalke reach the semi-finals.