The 36-year-old midfielder prioritised his club future after leaving Chelsea following a 13-year stint in June.
"I've had a bit of time after the World Cup, which was obviously a huge disappointment," Lampard said at his unveiling in Brooklyn.
"I now need to think about England and think about what I want to do with that.
"I haven't got a complete answer, but now I know where I'll be playing my football next year I can make that decision."
Lampard had no hesitation in moving to Major League Soccer, but with the season not beginning until next spring he may make a temporary move in the meantime.
He added: "I'm going to keep fit, that's the main thing. How I do that is not clear yet.
"I'm going to sit round with people at the club and sort that out."
Lampard became the fourth player to sign for New York City FC, the MLS' 20th expansion franchise, and insisted the switch was not a gamble despite joining a new club in a still-emerging league.
"What professional move doesn't have risk with it?" Lampard added.
"It's not a risk. It's a challenge. I can be in the middle of that challenge.
"I want to make New York City a team that New Yorkers are proud of. And I will do my best to do that."
Lampard made 649 appearances for Chelsea, scoring a club record 211 goals, since signing from West Ham in 2001.
He signed a one-year contract extension with the Blues in May 2013 after mulling over a move to Los Angeles Galaxy, who he will now play in opposition from next spring.
Lampard, who won every club trophy on offer with Chelsea, added: "Why not choose New York City? It's a very exciting challenge for me in life terms.
"I've seen the vision, a real long-term plan and I wanted to be part of that. I want to test myself, I want to carry on challenging myself, I want to be that leader, and not just on the pitch, but someone off the pitch.
"I had a fantastic 13 years at Chelsea, I can look back at that with immense pride.
"(But) it was a good time for myself and Chelsea that I moved on."
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