The Serie A side eventually won 3-2 against Trapani Calcio, but Ranocchia would have preferred not to deal with a nervy final few minutes after the Serie B side's second goal.
"We can't ever let our focus drop," Football Italia quotes Ranocchia as saying. "We still don't have the experience and haven't settled in enough to be able to manage the game.
"We can't stop at all. They attacked us, but we created chances. Plus, many of us haven't played very much and we still don't have a full 90 minutes in our legs.
"We didn't really risk giving away an equaliser, but still when it was 3-2 they were all getting into our box. That's why we can't let our focus drop any more."
Inter are currently fourth in Serie A.