Playing in the U-18 and U-21 teams, Leutwiler came through the ranks at FC Basel, but because Yann Sommer was first choice goalkeeper in front of him, Leutwiler was sent on loan at FC Concordia Basel in 2007, where he was more likely to get first-team football. At just 18 years of age he had much improving to do and a season-long loan spell at Concordia would have helped him to mature as a footballer. However, after only four games FC Basel cancelled the loan and took Leutwiler back as their first team third-choice goalkeeper because the transfer of Riccardo Meili fell through.