Ghana right back Phil Ofosu-Ayeh has been ruled out for four months after undergoing ankle surgery.
Ofosu-Ayeh, 25, is yet to feature for the club after signing on a free transfer in the summer from German second-tier side Eintracht Braunschweig.
The one-time Ghana international has been plagued by an ankle problem since the start of pre-season and underwent surgery this week, ruling him out for up to four months.
"Phil has a tough moment in his career. He began well (in pre-season), he got injured and has finally had surgery a couple of days ago," says manager Nuno Espirito Santo.
"It's going to take a while. Unfortunately he's going to be out for a while. I can tell you he won't miss all the season. The first verdict was three or four months."