Leno joined Cech and David Opsina at the Emirates as he completed his move from Bayer Leverkusen last month and is unlikley to be content with a place on the bench.
However, former England international Seamn believes that Cech's experience will ensure that he retains his starting spot ahead of the start of the new season.
"He [Cech] has still got great qualities and it isn't like he has had a bad season or anything, he still produced," Seaman insisted.
"Obviously he is getting older but your game adapts, that is what I found, you might not be as sharp as what you used to be but your experience gets you into the right positions."
Ospina has made just 11 Premier League appearances since joining Arsenal three years ago and Seaman thinks that Lwno's arrival could push him towards the exit door.
"I don't think Ospina would be quite happy being a No 2 because he has been that for quite a while," he admitted.
"He might even be a No 3 so I would imagine David wants to play football, you can't spend a big chunk of your career being a reserve. You've got to go out there and see how good you are."