Mackail-Smith, 26, told BBC Radio Cambridgeshire: "As soon as Darren was mentioned as successor to Gary Johnson expectations were raised.
"But everyone has to be patient as we can't get too carried away."
Posh are fifth in the League One table, but remain within reach of the automatic promotion places.
Mackail-Smith says he shares the fans' excitement at Ferguson's return, and insists a top-two finish has to be their aim.
"We're in a good position to get promoted, but we'll need time to adjust to playing under Darren Ferguson again," he said.
Goalkeeper Joe Lewis is continuing between the sticks despite having been placed on the transfer-list by request.
Mackail-Smith says the rest of the squad are staying focused on the job in hand.
"Joe has been fantastic throughout the time he's been here and he wants to be playing at the highest level possible," he said.
"If he has the chance to go and play in the Premier League then that's great, but either way the rest of the lads will get on with it."
Source: BBC Sport
Source: BBC Sport