FC Zurich midfielder Blerim Dzemaili will be out for around six months after rupturing cruciate knee ligaments.
Dzemaili, who will join Bolton Wanderers on a two-year deal in the summer, has played his last game for the Swiss league leaders.
The 21-year-old sustained the injury in training on Saturday and is to undergo surgery before beginning a long rehabilitation process.
Dzemaili agreed a summer switch to Bolton in February along with French Under 19 international defender Gerald Cid.
However, the Swiss international looks unlikely to make his debut for Sam Allardyce's side until October at the earliest.