The ex-Watford forward has been unable to train since Swansea's 2-1 win over Newcastle, and was not in the matchday squad for Sunday's draw with Liverpool.
Swans boss Michael Laudrup said: "He is not available. We really don't know (what it is). He has been sick for nearly a week now, he doesn't feel well and he has been feeling dizzy.
"We have had three or four players with that, but they are all back in training, but Danny is still ill so he is ruled out for the game tomorrow."