Spanish World Cup winner and double European champion Xabi Alonso is set to retire at the end of the season when his Bayern Munich contract expires, a report in Germany said.Leaders Bayern kick off the second half of the Bundesliga season at Freiburg on Friday in their bid for a fifth straight German league title with the 35-year-old Alonso poised to end his playing career in June. It would mean the German giants could lose significant experience for next season with club captain and ex-Germany skipper Philipp Lahm also reportedly considering retiring in June to take over as Bayern's team manager.According to Sport Bild, Alonso has already told club bosses he does not want to sign a contract extension. Having joined Bayern for the 2014/15 season, Alonso is bidding to finish with a third straight German league title with Munich currently three points clear in the table.