The Rhinos have been training across the city of Leeds since the river Aire burst its banks at Christmas.
Chief executive Gary Hetherington told BBC Radio Leeds: "It is looking like £1m in total. It has caused massive disruption.
"But sport throws up all sorts of challenges and this is another one."
All seven training pitches and the main building at the Kirkstall site the Rhinos share with rugby union side Yorkshire Carnegie were contaminated by flood water at the end of December.
The Rhinos, who begin the defence of their Super League title against Warrington on 4 February, say that 80 members of staff based at the site, plus 120 players, have been kept out for the last month.
"We couldn't get anywhere near the site," said Hetherington.
"When we were able to access it, the reality hit everybody. The whole site was under water. The changing rooms, medical rooms and gymnasium, and all the equipment was completely destroyed.
"All the pitches are contaminated so they need to be dug up and reseeded. The 3G pitch needs to be replaced. The buildings need to be replastered, all the floors need to come up.
"It will be the best part of six months before we can use the grass pitches and gymnasium."
Leeds Rhinos rugby league team face a £1m bill for flood damage that could keep them out of their training ground for a further six months.