The 34-year-old midfielder believes that no one is an automatic selection and that not one of his teammates is sure whether they'll be facing City at Wembley.
Lampard has played 43 times in all competitions this season, bagging 19 goals in the process.
"I don’t think anyone is an automatic selection with the manager at the minute as we see because there are lots of games and he’s changing it regularly," Lampard told The Daily Telegraph. "We’re not sure we’re playing on Sunday. I’m like everyone else: I want to play every game but it’s not possible."
He added, "That depends on how you’re playing and what manager you have, and relationships, and things change."
Chelsea is aiming to reach their fourth FA Cup final in the last 10 years and are in great form in the competition, having won 23 of their last 28 ties.
"I don’t think our record gives us an advantage, particularly in a game against Manchester City’s quality," he explained. "If they’re at their best and we’re not, they’ll probably win the game and vice versa."