Sky Blues boss Peter Reid had hoped to sign Norwich City's Malky Mackay, but turned to Leacock after the Scottish international rejected the move in favour of joining West Ham United.
The 20-year-old centre-back has not featured in Chris Coleman’s line-up this season but played four Premiership games last term, during which the team kept three clean sheets.
Leacock is expected to go straight into the Coventry side for Saturday's trip to Leeds United.