Martin O'Neill fears Andy Johnson could return to goalscoring form against Aston Villa.
The Everton striker missed two penalties against Metalist Kharkiv on Thursday night to extend his barren run without a goal.
Johnson has not scored since March but O'Neill suspects the England man could come out of his slump at Villa Park on Sunday.
"His recent run without a goal could be pretty bad news for us," he said.
"Johnson is a good player who causes you enough problems during the course of the game without getting on the end of things. He did that at Goodison Park against us last season about five times.
"I must admit that I didn't realise he had gone so long without a goal.
"We all know that strikers thrive on goals and if they go three or four games without scoring you know that in their minds they are thinking that run could be extended.
"That is why scoring boosts their confidence and the next thing is they know that they can also score from the next opportunity three minutes after getting a goal."