Johnstone played on Saturday as Bruce's men were beaten 2-1 by Shrewsbury Town in a pre-season friendly and looks set to be be the club's number one for 2017-18.
Some strong performances for Villa last season showed his potential, however the United loanee was also guilty of high-profile mistakes that had the Midlands fanbase questioning him at times.
Johnstone spoke of his delight after he put pen to paper on his loan deal, he said: "I am delighted to be back".
The Manchester United goalkeeper has now been out on 10 separate loans from Old Trafford
With David De Gea and Sergio Romero ahead of him in the pecking order, making the breakthrough at United will be a hard task for Johnstone, while young goalkeeper Joel Pereira, who travelled on the club's pre-season tour of the United States, is also highly rated by Jose Mourinho.More news: Milan interested in Bayern's Renato Sanches - Rummenigge