Jessica Harrington will carry out a series of tests on Sizing John following his below-par effort in the Leopardstown Christmas Chase.
The Cheltenham Gold Cup winner failed to fire in the Grade One contest, for which he was sent off the 9-10 favourite, trailing home a well-beaten seventh behind winner Road To Respect.
Following the race the seven-year-old was reported to be distressed and found to be clinically abnormal after being examined by veterinary staff at the track.
Harrington said: "The official report said he was a clinical abnormality after the post-race examination. He is sound now and his heart was OK.
"Basically he got slight hyperthermia and he got too hot. As soon as he cooled down, he was grand.
"I won't know anything else until I run some blood tests on him when I get back."
