Portsmouth boss Adams admits Defoe going under knife
Adams initially hoped the £7.5million striker, whom he is desperate to keep despite the fear that bigger clubs will bid for him in the January transfer window, would be fit to face Hull.
But Adams admitted: "He's had this problem before and we've got to get it sorted out for him. We will.
"He is seeing a (specialist) guy on Monday and we'll know more about his situation then. I'm not a doctor so I can't really comment at this stage but we'll see.
"No, he won't play against Milan. And Lassana is seeing other specialists (on) Monday, Tuesday and Wednesday. So he's got to be a doubt with his ankle. We're covering all bases with them, making sure they get the best.
"Niko's come back from his specialist with a good report but he got a bang on the ankle where he had the operation (in August) and I won't take chances with anyone who is not 100% fit.
"I did that with myself as a player and you can't do yourself justice."