Rafa Benitez is waiting to discover the extent of the injury which saw Aleksandar Mitrovic taken to hospital.
Mitrovic was stretchered off early in Newcastle United's 1-1 FA Cup draw against Birmingham City at St Andrew's this afternoon.
The striker suffered a cut in a collision with goalkeeper Adam Legzdins as Daryl Murphy gave Benitez's side a fifth-minute lead.
Lukas Jutkiewicz levelled three minutes before the break to set up a replay at St James's Park on Wednesday January 18.
Mitrovic needed oxygen as he was taken off the field by medics.
"It was a cut," said Benitez. "He went to hospital. It was obviously not very good, because we had to substitute him straight away. We will see how long (he is out)."
Benitez does not think the injury will have a bearing on his plans for this month's transfer window.
Asked if it was a long-term injury, Benitez said: "I don't think necessarily long term. For us, it doesn't change too much our decisions (on transfers).
"We will see how he is, but we were thinking before and it is the same situation.
"For him it is a blow. Hopefully, he will be fine, but in terms of the transfer window we were not considering anything and hopefully it will be the same."
On the replay, Benitez said: "It’s not ideal. Not for them, not for us, but we have to manage."
Newcastle's Championship game against Brentford at Griffin Park has been brought forward to Saturday, January 14 as a result of the replay.