Japan have conceded a total of 176 points and 28 tries in their three games so far, mostly due to the 107-6 trouncing New Zealand meted out to them.
But a dogged display from Japan in their last outing - a 28-12 defeat to Samoa - has given McAleese has plenty of food for thought.
"Japan are not what people would expect. They ran Argentina close and while New Zealand beat them well, Samoa just got past them.
"They are not small, indeed they are very physical and have impressed more and more through the tournament," McAleese said.
"They have a big pack which can compete with anyone and indeed they drove Argentina some 20 yards. We are certainly not taking them lightly."
Samoa's bonus point win played a part in sending Ireland down to ninth place in the final pool stage table. McAleese's charges lost 31-5 to a physically-imposing South Africa last Friday and they are particularly keen to bounce back and finish out the tournament with two victories.
"Of course it is a big disappointment finishing in the bottom tier," the coach told the Newsletter. "But we will get on with it and we have two big games to come, the first of those against Japan and then hopefully a 9th-10th play-off against either Scotland or Fiji.
"(For this game) we're bringing a bit of freshness into the side, but that will also give those who have been involved a chance to freshen up as well. Managing the players is an integral part of a tournament of this type when the turnover is so quick between games."
The Irish management have made a total of six personnel changes for tonight's clash with Japan, with plenty of movement in the back line.
Niall Morris has gotten over a foot injury to start at full-back, with Jamie Smith switching to centre. Eoin O'Malley, who lined out in midfield in Ireland's three games to date, steps in for Scott Deasy at out-half - his half-back partner will be Kris Greene who replaces Harry McAleese.
Up front, Ian Leonard and Michael Sherry will get their first starts in the front row, alongside the returning Matthew Nelson, while Kieran Essex makes way for Patrick Mallon in the back row.
"We took a lot of things into account (when selecting the team), including performance in the last few games. We also have to deal with a few minor injuries and look at the mindset of the players, particularly after three tough games," McAleese explained.
** Tonight's match between Ireland and Japan at Shaw's Bridge, where England and Argentina will meet in the earlier play-off tie (5.30pm), is an ALL-TICKET affair. Tickets are no longer available to purchase online, but they will be available to buy at the gate **