The Cheltenham Festival has been dealt a blow with Flemenstar suffering a lung infection and Sizing Europe scratched from the Gold Cup.

Trainer Peter Casey said Flemenstar was "very unlikely" to run at Cheltenham next month after the diagnosis on Monday following his second to Sir Des Champs at Leopardstown.

"He'll be out for two to three weeks," Casey told the Press Association.

"It's a bad lung infection.

"He's going to be all right in the long term, but I would say Cheltenham is very unlikely now.

"The jockey (Andrew Lynch) thought something was wrong on Saturday and it looks like he was right."

Henry de Bromhead said it was "50-50" which race Sizing Europe would now contest after he was officially scratched from the Gold Cup.

The Queen Mother Champion Chase and the Ryanair Chase remain the two options for the talented 11-year-old.

Sizing Europe is already a dual winner at the Festival, lifting the Arkle Trophy in 2010 and the Champion Chase in 2011 as well as finishing second in the latter event last year.

"He's out of the Gold Cup and we've put him in the other two for the moment," De Bromhead said.

"We've no idea which race. It's definitely 50-50 now.

"We are always looking forward to Cheltenham when he's running. He's been super.

"He seems in good form, he seems well and we're happy with him at the moment."