Goalkeeper Forster is being linked with Portuguese giants Benfica while captain Brown's future has also been questioned but Lennon says he is completely committed to the Hoops.
"It's a rumour that's spread in the last few days. I don't know if they're trying to unsettle the player," said Lennon in the Daily Record.
"There has been no concrete enquiry for him. He's not for sale and there's no way I'd let him go.
"It doesn't surprise me but he's not for sale."
He added of Brown: "He is very settled here. He is midway through a long-term contract at the minute and has never made any moves to me about wanting to go.
"He's got a young family now and I think he sees ending his career here."