But Ferguson insists both Lewis and Mackail-Smith would only leave if the price is right for Posh.
"I suppose you never know, but Craig is concentrating on the job at hand and is doing a very good job for us," he said.
"If someone comes in with a bid which matches our valuation for Craig or any other player for that matter then we'll do what's best for the football club.
"We've had speculation about Joe Lewis, Craig and George Boyd and it won't be going away because they've all been doing well."
On Tuesday Mackail-Smith said he was not angling for a move away from London Road.
"If the club decided the bid's right I'll decide what to do then," he explained.
"But I am a Peterborough player and I'll concentrate on scoring goals for the club.
"Unless there's something solid and the club come and tell me something's happening then I'll start listening.
"But until then it's just a case of concentrating on my football.
"I want to be playing at the highest level and obviously I've got to keep working hard at Peterborough."
Meanwhile Jonathan Obika, Kieran Agard and Adam Clayton have had their loan spells ended by the club and have returned to Tottenham, Everton and Leeds respectively.
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