Does it constitute polytheism (shirk) if a sheikh, addressing his disciple who is traveling to Europe, says: "My son, if your soul tempts you to commit a sin there, then remember your sheikh, and Allah will avert this evil and indecency from you"?

This act is a great evil and polytheism (shirk) with Allah, because it is an appeal for rescue to the shaykh. What is obligatory is to remember Allah and ask Him for help and success and to hold fast to Him. Guiding disciples to worship shaykhs and resort to them for fulfilling needs and dispelling distress is major polytheism (shirk akbar). A Muslim must fear Allah and turn to Him, Glorified be He, in matters of concern, and ask Him for help and success.