Celtic have signed Germany Under-21 midfielder Mika Baur from Paderborn for an undisclosed fee, with manager Martin O'Neill praising the Scottish champions' "perseverance" in pursuing the 22-year-old. Baur has signed a four-year contract with the option of a further 12 months, having helped Paderborn end a six-year absence from the Bundesliga as they finished third in the second tier last season.

"Mika's club in Germany were very keen to keep him, which I fully understand, as he played such an important role in their Bundesliga promotion," O'Neill told his club website. Baur made 36 appearances last season, scoring four goals and providing six assists, including their play-off win over Wolfsburg.

Paderborn sporting director Sebastian Lange said: "As a key player from our promotion season, we would have loved to keep Mika. When he expressed his desire to move to Glasgow Celtic, we didn't want to stand in his way." Baur, whose father Markus was a German handball international, explained his decision: "I want to win something and I think I'm in the right place for it."

Baur becomes Celtic's fourth signing of the summer transfer window, while fellow midfielder Arne Engels is wanted by West Ham United.