The 26-year-old was forced off during the goalless draw with Crystal Palace last Saturday due to an ankle injury, but Poyet refused to say whether the striker would be out for the season.
"We are still assessing. I think next week, we are going to have the final decision on him, but he is not fit for this weekend and we are trying to see what we are going to do," the Uruguayan told reporters.
"It was quite swollen, so it's difficult to do all the tests. When you do the MRI tests, there is always some swelling around and it's not very, very clear, so we are trying to be calm and assess it properly next week."
Sunderland travel to Carrow Road to face Norwich City on Saturday afternoon.