The 33-year-old, of Northampton, was sentenced to six months in prison after admitting sending the letters to Northamptonshire Police in an attempt to avoid speeding convictions.
Sentencing the former Premiership footballer at Northampton Crown Court, Judge Richard Bray said: "A custodial sentence is necessary for this type of offence which strikes right at the heart of justice. It would completely send out the wrong message if I did not hand out a custodial sentence."
McKenzie, who retired from professional football in December, was also handed a 18-month driving ban.
Source: PA
Source: PA