Lampard, 35, was released by Chelsea at the end of last season and although he is expected to play on at club level, Mourinho believes that the time has come for him to retire from the international game.
"I think the World Cup is the perfect way for somebody with more than 100 caps (104) to finish his career in the national team," Mourinho said.
"I told him that: 'Don't go more than the World Cup. The World Cup is the right moment to finish.'"
"So (it's the) right moment. And after that, he will be free just to play for a club and let's see what is his decision.
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"But he's a man to play a major role in a team, not like happened in the last year -- playing sometimes, sometimes not playing, playing 60 minutes, not starting every game.
"I think for him, for his mentality, for his personality, it's better to get a club and probably a competition where he is really the top man."
"It's very hard to get the words out to say that," he said. "I won't say it at this point. I've never said it before and I've had plenty of opportunities to do so.
"Most players finish with England in their low thirties at the most. I've had some of my most enjoyable England years in the back end, in the last two years.
"When you're young you don't always appreciate being in the squad, the ambiance around the squad. That's why I won't write myself off yet.