The Everton midfielder has been recovering from a broken metatarsal, suffered at Sheffield United in March.
And in his first game back for the Toffees last night against Werder Bremen he was taken off after 61 minutes after falling awkwardly - the worry being that he had damaged the same foot again.
Cahill had an X-ray earlier on Wednesday before Everton announced on their website, that he was being referred to a specialist.
Everton's assistant manager Alan Irvine was considered with his view on Cahill after the 2-2 draw with the Germans.
He said: "He felt his foot again which obviously is a bit of a worry. He landed on it awkwardly which probably frightened him a little."