Manchester United boss Sir Alex Ferguson has warned Rio Ferdinand that he needs to prove his fitness this season.
Ferdinand started only 19 Premier League matches in their title-winning campaign last term.
And Ferguson has bolstered his central defensive options by signing Phil Jones, to go along with Chris Smalling and Jonny Evans - who were already pushing for places.
Now Ferguson says he has the 'best three young centre backs' in England ready to come in for Ferdinand.
"Rio will have to stay fit, that is the key for him," Ferguson is quoted by the Sunday Mirror.
"As he gets older, he won't play all the games because we have Chris Smalling, Jonny Evans and Phil Jones who are the best young centre backs in the country.
"Any one of them can come in."