Roger Varian will make a late call as to whether to let Defoe take his chance in the Tattersalls Gold Cup at the Curragh on Sunday.
The Newmarket trainer plans to walk the course on the day of the race before making his decision.
Speaking to Tattersalls, Varian said: "Defoe has been declared to run in the Tattersalls Gold Cup, but his participation will depend on how quick the ground is and I intend to walk the course on Sunday.
"He has certainly earned the return to Group One company, winning at Group Two and Group Three level this season, while I don't think the drop back in trip would inconvenience him on a track like this.
"He is training nicely and he would have a very live chance on form, but I wouldn't want to compromise his season by running him on an unsuitable surface and a final decision over his participation will be made at the last minute."
Defoe is a prolific winner, having struck in six of his last seven races - with his only reverse coming in the St Leger at Doncaster.
This term he has already won the John Porter and Newbury and Newmarket's Jockey Club Stakes.
The race centres around the potential clash between Defoe and Aidan O'Brien's Cliffs Of Moher. The Galileo colt was runner-up in the Derby last year but then lost his way after a rough passage in the Eclipse. O'Brien has nursed him back to his best and he won the Mooresbridge Stakes comfortably last time out.
Success Days, second in the Mooresbridge, Lancaster Bomber, who ran in the Lockinge last week, and Joseph O'Brien's Reckless Gold complete the field.
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