Senior, who played in all three Tests against New Zealand this autumn, would be much sought after if he was on the market. However, Sheffield's recruitment this winter had made him keen to stay at his only professional club.
"He is one of the game's top centres and by the end of his contract he will be the best in the country," the Sheffield coach, John Kear, said.
Bradford have filled their last overseas spot by signing the experienced former Canberra centre or second row David Boyle from the defunct Gold Coast Chargers.
Either of the consortia which could take control of the struggling Doncaster club will be have to reapply for membership of the League.
"We are becoming increasingly concerned about the future of the club," Tunnicliffe said. "If there is a take-over, we will be exercising our rights by asking them to reapply."
Doncaster are included in the fixtures for next season, but the League will want evidence they can fulfil their programme before confirming their participation.Reuse content