Steve Bruce says that Jetro Willems' rehabilitation programme is now in the hands of Eintracht Frankfurt.
The Dutchman - who could be out for nine months - ruptured his cruciate ligaments in the clash with Chelsea at the weekend after an injury which ruled him out until the end of his loan term on Tyneside.
For now the injury has dashed hopes of a permanent move but Willems has vowed to fight on.
But Newcastle are likely to remove Willems from their Premier League squad to free up a space for a replacement.
However, the next step is down to the Bundesliga club.
Bruce said: "He's their player.
"The parent club will always have the last word on it.
"Whether he is operated on in London, Germany or Holland, that will be decided by the player and his parent club."
Willems has posted a message to Newcastle fans after many posted their good wishes to the left-sided player ahead of his recovery.
He said: "I pledge to do everything I can, so it will not be my last game for NUFC!!!"
