Lomana Tresor Lua Lua has suffered a dislocated shoulder and will miss Olympiacos' match against Chelsea on Wednesday.
The former Newcastle and Portsmouth striker picked up the injury in Saturday's league match against Asteras Tripolis and is now set to be sidelined for six weeks.
Lua Lua sat out the first leg of Olympiacos' UEFA Champions League tie with Chelsea due to a foot injury.
The game finished goalless to give Olympiacos hope ahead of the return leg at Stamford Bridge.
But news of Lua Lua's injury will come as a major blow to supporters of the Greek champions.
"The player's left shoulder has been put in a special cast and he will be re-examined on Monday before we decide on what treatment will follow," said Olympiacos in a statement.