Kelly was snapped up from Liverpool.
"Martin's been through some injuries like a lot of young players do and he wasn't playing regularly but you don't suddenly become a bad player overnight," said Parish.
"We figure that it's a risk worth taking. We can't go and pay up to £10m for players in those types of positions. We look at that kind of deal and think yes there is a risk but the risk is really outweighed by a big upside for us."
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