Brentford admit Jay Dasilva has suffered a knee injury setback.
A hamstring injury has kept the midfielder out for most of the season and now it's the knee that's bothering him.
Bees medical chief Neil Grieg said: "Tests have shown severe damage to ligaments in his right knee, which will require surgery to repair.
"Following dialogue with leading knee specialists in the UK, Josh will now undergo a short period of preparation before the operation takes place, and no time frame for his rehabilitation has yet been discussed.
"He has previously shown an exceptional attitude in relation to rehabilitation, and we have full confidence that he is able to come back from this setback."