St. Pauli's new winger Ryo Miyaichi has sustained a left knee injury and undergone surgery, the German second-division side announced Thursday.
Miyaichi, who joined the club last month from Arsenal, tore his anterior cruciate ligament during a preseason friendly against Spanish side Rayo Vallecano on Saturday and went under the knife. No return date has been set.
The 22-year-old's career has been blighted by a string of injuries after joining Arsenal in December 2010, with the twice-capped Japanese injuring his right ankle ligament twice while on loan at Wigan in 2012-13 season, limiting him to just four league appearances.
Miyaichi made only league appearance for the Gunners the following season, but suffered a serious hamstring injury late in the campaign in March. He was loaned out to Dutch side Twente last season, but made only six starts and 10 appearances in the league without scoring a goal.
Miyaichi signed a three-year deal with St. Pauli, which is targeting promotion back to the Bundesliga, where it last competed in the 2010-11 season.