The star eight-year-old is hot favourite for the two-mile championship, but has developed lameness in a leg.
Trainer Nicky Henderson said he will have a more definitive idea this morning of whether or not he runs at Cheltenham.
The Seven Barrows handler said in a statement posted on his Twitter account: “Altior was unfortunately lame this morning in his near-fore leg and we have located some pus in the frog (of his foot).
“He was still able to exercise in the water treadmill this morning, which he regularly does anyway, and a poultice will now be applied and left on overnight to draw out the pus.
“The foot will also be ‘tubbed’ (stood in salt water) at regular intervals and the shoe will hopefully be replaced first thing tomorrow morning.
“Both our vet and farrier are working very hard and are more than hopeful that he will even be able to canter tomorrow and therefore confident he will be clear to race on Wednesday.
“Obviously we will monitor the situation and keep everybody up to date with his progress, but there will nothing more to say until tomorrow morning.”
BREAKING NEWS ON ALTIOR & WE HAVE A DREAM pic.twitter.com/SewLygV0bX— Nicky Henderson (@sevenbarrows) March 12, 2018
Should he recover in time, Altior will face Douvan after the eight-year-old was given the go-ahead to take his chance in tomorrow’s feature race.
Trainer Willie Mullins and owner Rich Ricci had suggested on Sunday they might avoid a clash with their other hope, Min, and wait for Thursday’s Ryanair Chase.
However, he was among nine horses declared for the two-mile championship.
The only withdrawal at the 48-hour final declaration stage was the Mullins-trained Un De Sceaux, who is set for the Ryanair.