Clarke-Harris has signed in time to be included in Saturday’s matchday squad for the trip to Rotherham United.
The 18-year-old can play in attack, on the wing and has also featured at left back.
He has made one substitute appearance for Coventry City in the League Cup as a 16-year-old breaking the record as Coventry’s youngster ever debutant.
He was released in the summer after failing to secure a pro contract with the Sky Blues before signing a two-year contract at London Road with the Posh where he is yet to make a first team appearance.
And manager Paul Sturrock was delighted to have secured their youngsters services for an initial one-month loan deal.
“We’re pleased to have Jonson on board for the next four weeks,” Sturrock told the official website.
“He’s an exciting talent and we’ve watched him twice so we will see how he gets on in the next month.”
Meanwhile, Sturrock also confirmed that he is close to securing the services of a central midfielder.
The Scot has been working on a deal to bring in a target but believes it may now happen early next week.
“Obviously a centre midfielder is a priority and so you might consider it strange we haven’t signed one yet,” he said.
“We’ve been in talks for a few days with a club this week but I would be surprised now if we get it done before the weekend.
“We specifically want this individual though so I’m prepared to wait until next week if necessary when we should finalise things.”
Jonson Clarke-Harris will wear the number 12 shirt vacated by Kane Ferdinand who joined Peterborough in the August transfer window.