Lech Poznan have been ordered to play eight games next season without spectators because of rioting and brawling by fans.
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Poland under-21 international Bednarek has agreed a five-year contract.
Celtic eased past Stjarnan in their Champions League second-leg qualifier, while Astana upset Maribor to progress through to the next round.
Two of last season's Champions League group-stage underdogs got off to a rough start in the first leg of the second qualifying round on Tuesday.
Known as the "Polish Benitez", Maciej Skorza has Lech Poznan poised to win the Polish Ekstraklasa and attempt a run in Europe, writes Michael Yokhin.