All three will be out of contract when their current deals run out on 30 June.
Britton has had seven years at Swansea but is out of contract next summer.
People that are out of contract, we are struggling to find money to renew them.
Diao, who was out of contract, will stay at the Britannia for another year.
Finn Kovalainen is also out of contract and under pressure at McLaren after failing to realise his early potential.
Miller, 31, played under McLeish at Rangers and is out of contract at the Scottish club in the summer.
Campbell is not the only first team regular out of contract at the end of the season.
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The 23-year-old, tipped as a future England captain, is out of contract with Wasps in the summer.
The future remains uncertain for Kyle, the 28-year-old Scotland striker who is out of contract in May.
"So for the first time ever I will be out of contract in the summer, " he said.
Centre-back Youl Mawene, who is also out of contract in June, is set to discuss his future soon.
The 40-year-old central defender is out of contract with the Scottish champions at the end of the season.
The 35-year-old defender is out of contract after playing for Arsenal in the second half of last season.
Rosberg, son of 1982 Formula One world champion Keke, is out of contract with Williams at the end of the season.
First, most transfers 86% involved players who were out of contract, which means there was no exchange of money between clubs.
Eleven players are out of contract and decisions still have to be made over who they want to keep.
Warnock has guided the Blades to second place in the Championship but is out of contract in the summer.
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The Stutes advertised the position, stating Lewer was out of contract but welcome to re-apply for his old job.
Cooke rocked Hull FC earlier this week by handing in a transfer request, claiming he was out of contract.
He is out of contract this summer and has made no secret of his desire to remain at the club.
McNamee is out of contract next summer and the former Watford youth player admits it's been a distracting few months.
Hughes is on the lookout for a challenge to Yves Ma-Kalamby and Mallo is out of contract with the Bairns.
Lewer is out of contract in the summer and the club have been in contact with former boss Steve Fallon.
Jan is out of contract - he is free to seek other employment and I'm pretty sure that's what he will be doing.
Harsley, 29, is out of contract and is one of four players to be offered new deals by manager Lee Sinnott.
"We've got a situation where we have six out of contract and we haven't agreed a contract with any, " he said.
The 31-year-old, who is out of contract with the French club in the summer, has agreed a two-year contract at Ibrox.
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Meanwhile, former Zimbabwe all-rounder Neil Johnson has failed to impress in two years in Southampton and is now out of contract.
Wayne's out of contract, he's one we'd liked to keep but it might be much more difficult to do that now.
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The 12-goal striker, who turns 24 this month, is out of contract this summer and could leave on a free transfer.
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