Killen must also do 200 hours unpaid work and sign the sex offenders register.
He was due to be sentenced yesterday, but the case was re-listed for today.
New Zealand-born Killen represented his country in the 2010 World Cup after playing for Middlesbrough and Celtic and starting his career with Manchester City as a trainee.
His playing career also included stints at Hibernian, Norwich, Oldham Athletic, Port Vale and Wrexham.
Defence counsel Lisa Judge said that Killen, of Adlington, near Macclesfield, had 'no relevant' previous convictions.