McDonald moves to the League Two title chasers for the maximum 93-day period, although the Sky Blues have the option of recalling him after 28 days.
The former Norwich trainee has made 16 appearances for Coventry this season and scored three goals, including a last-minute winner at Oldham.
"I think it is a good move for him as he needs to get some minutes on the pitch," said Sky Blues boss Mark Robins. "He's going there to play and rediscover his goal-scoring.
"We are hoping he does well and he produced great form at Gillingham in a previous spell with the club, so it should be the right atmosphere for him to build up some form."