The Canaries keeper has been in fine form since being given the No.1 jersey but is wary of the threat to his position posed by his almost-fit England international team-mate
Bunn arrived at Carrow Road in August from Blackburn, and was signed initially as back-up to Ruddy, but was handed his place between the sticks when the England international got injured in November.
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He told BBC Radio Norfolk: "I didn't expect to come into the team straight away but unfortunately for John he's been out with a long injury.
"He's due back soon so I've got to be on top of my game to keep him out. I love playing. It's been a while since I've played quite a few games.
"From a goalkeeper's point of view it's always good to keep clean sheets, that's why I'm there, to make saves. Hopefully I can keep another clean sheet in the next game [against Sunderland]."
Bunn has kept four clean-sheets in his last eight appearances, and Canaries boss Chris Hughton is full of praise for his stand-in goalkeeper.
"He's done ever so well," he added. "He's got that little bit of composure about him at times.
"Because he's not one of those really tall goalkeepers he has got that agility. He had to show good quality in his kicking and I think overall he's done well for us."