Jessica Harrington reported Sizing John to be showing no ill effects on Friday after his disappointing performance in the Grade 1 Leopardstown Christmas Chase the day before.
Sent off the 9-10 favourite, Sizing John finished only seventh behind Road To Respect and was found to be “clinically abnormal” following veterinary examination at the track.
Jockey Robbie Power reported the horse to have been distressed at the end of the race.
Speaking at Leopardstown, Harrington reported: "Sizing John was sound this morning. We had him fully checked out and blood tests were taken. It looks as if he just overheated for some reason during the race.
"We'll know more when we take more blood tests in four days' time. We'll just have to wait and see how he is and there's no point in talking about plans at this stage."
Sizing John was bidding for a fifth consecutive Grade 1 victory in Thursday's race. He won the Irish Gold Cup, Cheltenham Gold Cup and Punchestown Gold Cup last season and made a winning return in the John Durkan Memorial Chase at Punchestown this month.
Following his poor effort at Leopardstown the seven-year-old was pushed out to 8-1 to successfully defend his Timico Cheltenham Gold Cup crown in March. King George winner Might Bite took over favouritism and is a best-priced 4-1.