"He (Cech) has still got great qualities and it isn't like he has had a bad season or anything, he still produced," Seaman, who won three league titles at Arsenal, told the British media.
"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."
Cech's arrival from Chelsea in 2015 meant that David Ospina became the team's back-up goalkeeper and the Colombian has made just 11 Premier League appearances since then.
Seaman said Leno's move to North London could have an impact on Ospina's future at the club.
"I don't think Ospina would be quite happy being a number two because he has been that for quite a while," Seaman said.
"He might even be a number three 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."
Arsenal, who finished sixth last season, begin their league campaign against defending champions Manchester City on Aug. 12.
(Reporting by Shrivathsa Sridhar in Bengaluru; editing by Sudipto Ganguly)
