Newcastle boss Eddie Howe admits Joelinton could be sold.
The midfielder faces at least four months out after thigh surgery.
Howe said, "It's a massive blow for us.
"We knew when he did the injury it immediately didn't look good. We didn't know he'd be out as long.
"He's had a stop-start season. When he is fit and firing, there's no one like him and he brings a different dynamic to our midfield.
"He's a leader as well. He'll be a big miss."
On Joelinton's future, he also said: "It's a possibility [he could leave] but I hope that's not the case. I want him to stay.
"Before a player signs a contract he has to be happy with everything and so it's a possibility he'll be sold in the summer."