The American athlete, who finished second in the 400 metres hurdles at the 1984 Olympic Games in Los Angeles, denied two counts of contact with a minor for sexual offence, two counts of child abuse and two counts of child annoyance.

The 51-year-old, who was arrested by police last week, is facing seven years in jail if he is found guilty.

According to prosecutors, Harris sent the underage girl inappropriate messages between April and May of this year when he was track and field coach at Gabrielino High School in California.

The messages were discovered by a relative, who then reported it to police.

Harris has since been sacked from his coaching role by the high school.

"The police department has been working closely with the San Gabriel Unified School District following a report of alleged inappropriate contacts between the walk-on athletic coach and a district student," a police statement published by the San Gabriel Valley Tribune read.

"The school district and the police department are working together to ensure the safety of students remains of utmost importance."

The former athlete is the subject of a documentary entitled Crossing the Line, which details his struggles since his career on the track ended in 1996.

Following his Olympic silver medal winning performance on home soil, Harris ended the 10-year dominance of compatriot Edwin Moses in the 400m hurdles by beating his team-mate in Rome in 1987.

It was the first time Moses had lost a race in 10 years.

Disappointment followed at the 1988 Olympics in Seoul for Harris, however, as he crashed out at the qualification stage in the South Korean capital.

He then struggled with cocaine addiction and homelessness before he got clean and began coaching at high school level.