United States and Monaco striker Folarin Balogun will undergo surgery on his recently dislocated shoulder.

Speaking ahead of his team’s Champions League game at Arsenal on Wednesday, Monaco coach Adi Hütter said he did not know how long Balogun will be out for after the operation.

The forward was sidelined for about two months with the injury and returned to competition at the end of November. But he took a hit during a recent 2-1 loss to Marseille in the French league and had been in pain since, sitting out training sessions last week.

Balogun was in good form earlier this season, scoring for a third straight game as Monaco won 2-1 at Rennes on Oct. 5 before leaving the match with an injury. He suffered a dislocated shoulder and had to withdraw from a couple of matches with the U.S. team.

Balogun, born in New York and raised in London, signed a five-year contract for Monaco after leaving Arsenal last year.