Everton are currently in 16th place in the Premier League table.
Jagielka is reaching the twilight of his career now, while Mirallas has also gone past 30.
And Kilbane feels that Everton can no longer rely on the pair to drag them out of trouble.
The Toffees utilised both Jagielka and Kilbane in Everton’s latest match against Brighton & Hove Albion, but the duo were unable to inspire Ronald Koeman’s side.
Everton could only manage to pick up a 1-1 draw on the south coast, with their performance falling to impress again.
And Kilbane has expressed his doubts about Jagielka’s and Mirallas’ form improving.
He said: “Phil Jagielka has long been their go-to defender but he has had injury problems and I am not sure how much longer they can rely on him to be the man to hold their backline together.
“Kevin Mirallas came off the bench and did well in those areas against Brighton, including his part in the equaliser – he won the free-kick that led to Bruno’s moment of madness – but I would not pin all my hopes on him making a huge difference if he was given a regular starting role.
“From watching the Belgian in the five years since he joined Everton, he has not been consistently good when he has started games – he has always had a bigger impact as a substitute.”
Everton’s draw with Brighton has done little to relieve the pressure on Koeman, but it could have been worse for the Merseyside outfit.
The Toffees fell behind when Anthony Knockaert scored for Brighton, and only a late penalty from Wayne Rooney rescued a point for Koeman’s side.
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