Lampard penned a new 12-month deal earlier this summer.
Merson told Absolute Radio: "I don't think Frank's going to play all the time. I think Frank's a phenomenal, I mean he doesn't get the credit he deserves. I mean the goals he's scored year in year out since day dot, has been phenomenal. He's scores more goals than Xavi, Iniesta, all them people and they you know we never ever mention that. And that's the problem.
"I think he can play on and on. He scores goals. We looked at the end of the season against Villa, you know it looked tight, tight, tight and then bang, bang and then Frank scores two goals and it's game over. Thanks for coming."
Merson was talking to Absolute Radio's Ian Wright. Saturday at 5pm on 1215AM. For more, visit absoluteradio.co.uk/football.