Lionel Messi and Gerd Muller are fields apart

Barcelona's Lionel Messi.

And so it is finally settled: Lionel Messi is the GOAT.

Not the animal - although it sometimes appears that the Barcelona forward must have a couple of extra feet to retain the ball like that - but the Greatest Of All Time.

The title was clinched on Sunday night, many will argue, when he eclipsed the West Germany and Bayern Munich legend Gerd Muller's 40-year-old record of 85 goals in a calendar year.

Messi's second against Real Betis was his 86th in 2012.

That tally includes 56 for his club in the Primera Liga and 12 for Argentina, not least a hat-trick against some outfit called "Brazil" in June.

Oh yes, and he scored two more in a cup match against Cordoba on Wednesday and still has potentially another two games with Barcelona before 2013 arrives.

Not bad for a man with a month-old baby, eh?

And yet, despite the enormity of this achievement, can we really close the book on the GOAT debate?

You see, the problem with comparing footballers of different periods in time is that it does not provide an even playing field.

And I mean that literally, as well as metaphorically.

Messi plays on billiard table compared to those Bundesliga pitches of the 1970s, many of which looked like a war zone, when "Der Bomber" Muller was plying his trade.

Talking of nicknames, Muller's other was "kleines dickes Muller" - or "short, fat Muller" - bestowed upon him by his first coach at Bayer Munich.

That was how they dealt with physical imperfection back then.

You were mocked then told to make the best of it.

When Messi was noted to be short for his age, on the other hand, Barcelona funded an expensive course of growth hormone therapy.

Barca fans may call him "La Pulga" ("The Flea") but even this modest stature was medically assisted.

Messi was 11 years old when Barca signed him, by the way.

He was groomed for glory from a tender age, surrounded by the world' finest players, coaches, doctors and sports scientists.

Muller, on the other hand, was with TSV Nordlingen (then in the seventh tier of German football) until the age of 19.

Even Bayern were still in the second tier when he signed for the club in 1964.

Unlike Messi, Muller's skills were largely self-taught.

And on the subject of grooming, what about hair?

Muller played in an era of wild, flyway mop-tops which must have impaired players' vision for at least 10 per cent of the time.

They could only dream of the array of grip, Alice bands and firm-hold unguents available to the 21st-century professional.

Is it fair to mention wages here? I should say so.

Messi can afford to throw himself into every game, safe in the knowledge that his financial future is secure.

Back in the 1970s, however, players of a certain age had to be mindful of their legs, which were also required for their future careers as postmen or door-to-door insurance salesmen.

Oh yes, and if you think the two players were of a similar age when they achieved these feats, think again.

Messi is 25 now, which is considered a prime age. Muller was 27 in 1972, which - for a post-war generation raised on sawdust and powdered egg - was practically geriatric.

So, you see, context is everything.

Before declaring anyone the Greatest Of All Time, you must first ascertain they are not merely a Sporting Hero in an Era of Exceptional Privilege.

Or, to put it another way, you must sort the SHEEP from the GOATs.