Jessica Harrington remains at a loss to definitively explain the below-par performance of Cheltenham Gold Cup hero Sizing John at Leopardstown over Christmas.
The eight-year-old carried all before him in the staying chase department last season, winning the Irish Gold Cup and Punchestown equivalent in addition to his famous success at Cheltenham.
He made a fine reappearance in the John Durkan Memorial Chase at Punchestown in heavy ground last month, but could only beat Yorkhill home when a distant seventh of eight finishers in the Leopardstown Christmas Chase, for which he was sent off the odds-on favourite.
Following the result of blood tests, Harrington said: "We have not found any clinical reason so far from the tests carried out."
Owned by the late Alan and Ann Potts, Sizing John is the general second-favourite for a Gold Cup repeat in March behind Nicky Henderson's King George VI Chase winner Might Bite.