THE NICE thing about a side that has been together for as long as Milan has is that you can look into the history books and make an educated guess about how they will behave in any given situation.

Scroll back three years to 2004-05. Milan and Celtic are in the same Champions' League group. Going into the final head-to-head clash, the Rossoneri have already clinched qualification and have nothing to play for. Celtic need a win to get into the Uefa Cup. Sound familiar? Except for the fact Celtic need a result to qualify for the knockout stage (rather than the Uefa Cup) and the match is at the San Siro rather than Parkhead, it's deja vu.

Back then, Milan, predictably, fielded an under-strength side with just four regulars - Alessandro Nesta, Paolo Maldini, Andriy Shevchenko and Dida - in the starting XI. Alas, it was enough to fend off Martin O'Neill's men as the scoreless draw, coupled with Shaktar Donetsk's 2-0 win over Barcelona, left Celtic bottom of the group.

This time round, there is even more pressure on Milan to field the reserves against Celtic. For a start, the side are in free-fall in Serie A. They sit in ninth place, but the real shock has been their home form. They have yet to win a Serie A game at the San Siro. Indeed, they are the only side out of the 78 in Europe's Big Four leagues not to have won at home domestically this season.

That said, they have beaten both Shaktar and Benfica in Europe and this is a European clash. Yet the impression is that Milan have a certain fragility about them. They seem to have lost the ability to grind out results or, put another way, unless their superstars play out of their skin they find themselves dropping points.

Which is good news for Celtic because logic would dictate that Milan boss Carlo Ancelotti keep all his stars in bubble-wrap for their visit.

There are two reasons for this. The first is that - at least according to the Rossoneri spin machine - the squad's physical form is carefully calibrated to peak in the spring. The autumn months are, supposedly, spent achieving "maximum results with minimum efforts" before the side's true athletic prowess is unleashed in March. Three Champions' League finals in five years is meant to be a testament to this.

The second reason is that, simply put, this is an old squad and one which has struggled to rotate effectively this year. Andrea Pirlo, Alessandro Nesta and Clarence Seedorf have missed just one start this season, Kaka and Rino Gattuso have missed two. These players need a breather not least because Milan will shortly fly out to Tokyo for the World Club Championship.

And so Ancelotti will want to rotate. Alas, that's not an easy thing to do with this squad. Up front, Ronaldo is injured (again) and Pippo Inzaghi is getting over a bout of tonsillitis. With Brazilian wonderkid Pato Alexandre ineligible until January, Milan have just two able-bodied front men: Alberto Gilardino (who could use a rest himself) and Willy Aubameyang, who has yet to make his official debut at the club.

Things don't get much better in midfield. Here, it's not an issue of bodies as much as the fact the reserves have hardly had any playing time. Yoann Gourcuff, much hyped a year ago, has started just once this season. Emerson, brought back to Serie A amidst such fanfare, has made just two starts, a victim of age and injuries.

Massimo Ambrosini, a reserve on paper, has actually been almost ever present this season after Ronaldo's injury prompted the switch to a 4-5-1, so he could use some time off as well (especially in light of his moonlighting with the Italian national team).

Which basically leaves Christian Brocchi as the only trustworthy physically fit reserve likely to start.

At the back, two things appear certain: Daniele Bonera, Milan's jack-of-all-trades, will start. And so will a bunch of old guys, some combination of Giuseppe Favalli (35), Serginho (36), Cafu (37) and Maldini (40).

At most clubs, games such as these are an opportunity to blood youngsters. At Milan this is when the geriatric crew get their run out. But then, Milan are unlike most clubs.

And so, unless Ancelotti decides to play his entire youth side (something which, given Uefa's roster system for the Champions' League, he couldn't do anyway) it's highly likely the side facing Celtic on Tuesday night will feature a fair sprinkling of first-team regulars.

But that's not necessarily a bad thing for Gordon Strachan's crew.

Recent history shows that, in these situations, under-strength sides often do remarkably well. In the age of big squads and plenty of depth, matches such as these offer a rare showcase for quality players to strut their stuff. With the pressure off, they can prove to the manager they deserve to be in the side.

With Milan, however, it won't happen. Partly because they don't have much of a bench at their disposal. Partly because their first XI has been pretty much fixed over the past few years: an eye-popping performance from, say, Bonera or Brocchi won't help them displace the likes of Nesta or Gattuso. And largely because the players who will take the pitch - especially the veterans - have been long schooled in the art of pacing themselves.

They know the only way they can play football at the highest level well into their thirties is by holding back at certain times, conserving their energy for the games that really matter.

Throw in the fact that Celtic already beat the "real" Milan at Parkhead and Tuesday night really should not look that daunting for Strachan's crew.