Sunderland boss Martin O'Neill's defeat at Norwich City was compounded by a mystery injury suffered by Steven Fletcher.
The striker started the game in East Anglia but didn't feature in the second half.
O'Neill revealed: "Steven Fletcher was struggling for the last 10 minutes of the first half.
"He mentioned it during the break so we had to make the change.
"I'm not sure what the problem is, we'll have to wait and see."