The Spaniard had previously seemed to suggest the England pair would not be offered new deals at Stamford Bridge, but moved to quash speculation about possible destinations by suggesting the duo could well stay.
And while the players' futures may hang in the balance, the 52-year-old described Lampard as "part of the leadership" at the club, highlighting the importance of his experience within the squad.
"When I was asked the other day, maybe it was a misunderstanding or maybe my English was not good enough, but the situation I know is that they are finishing their contracts. Past that, I do not know," he told the club's official website.
He continued: "I know that Frank is happy here and he is a player that is part of the leadership, he is one of the important players, but I do not know about his future.
"So I cannot say yes or no, he will stay or he will leave, in January or even at the end of the season. At this moment, I do not know."
Benitez took over team affairs at Chelsea after club owner Roman Abramovich sacked Roberto Di Matteo following a disastrous 3-0 defeat to Juventus which leaves their hopes of defending the Champions League in the balance.
Since replacing the Italian, the new interim manager has taken two points from three games, which included a dispiriting 3-1 defeat away to London rivals West Ham on Saturday.
And while Benitez has not got off the best of starts at Stamford Bridge, he revealed that the board asked him about players coming in to the club during a meeting on Friday - but did not discuss departures.
"We didn't talk about any players going. The board were asking me about players coming but not about any players leaving," he added.
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