I disagree. The world cup is a unique challenge where you get taken away from your comfort zones and teams build solely fo suit your needs, and into a slightly alien environment with a small amount of games to rise to the occasion and knit a bunch together into champions. It takes a certain quality to succeed in that environment which isn't ever really tested at club level. On that basis alone the player who is the best ever needs to prove he can be the best at thid unique challenge too. On top of that, it is the games biggest and most important prize.
So yeah, for me, maybe not win, but a player must dominate world cups to be the best ever. Unless he plays for too small a nation. Messi doesn't.
Imagine if Ali never inspired his team to basketball's biggest prize. Or Ali didn't win his sport's. Or if the Australian cricket team never won the cricket world cup (they won it thrice).
Except that this isn't always true... Many great teams have been built around a core of players that played their club football together. See Spain 2010 for the most recent and obvious example.
Others include:
- the great Magical Magyars of the 50s of which 6 of the usual starting XI played for Budapest Honvéd (Grosics, Lóránt, Bozsik, Kocsis, Puskás, Czibor), all 6 started in the 1954 WC Final.
- "Garrincha's Brazil" that won in 1962, starting XI consisted out of 4 Santos players (Gilmar, Zito, Mauro, Pelé) and 4 Botafogo players (Nílton Santos, Didi, Zagallo, Garrincha) and after Pelé's injury in the 2nd game the balance went 3-5 for Botafogo with Amarildo coming in; these also started in the Final.
- the Total Football Dutch team of the 70s, based on Ajax players (Krol, Suurbier, Haan, Neeskens, Cruyff, Rep), all 6 started in the 1974 WC Final.
- the German team of the early 70s that won the EC and WC, based on Bayern Munich players (Maier, Schwarzenbeck, Beckenbauer, Breitner, Hoeneß, G. Müller), all 6 started in the 1974 WC Final.
- the iconic Italy team that won in 1982, based on 6 Juventus players (Zoff, Scirea, Gentile, Cabrini, Tardelli, P. Rossi), guess what, all 6 started in the Final.
- that great defensive Italy team that reached the final in 1994, based on 6 Milan players (Baresi, Maldini, Costacurta, Tassotti, Albertini, Donadoni); only 4 of them started in the Final (+ Massaro who also played for Milan but hadn't been a starter before the quarter-final).
- the exciting German team of 2010 (and now), based on 5 Bayern Munich players (Lahm, Badstuber, Schweinsteiger, T. Müller, Klose) and since then Mario Gómez has become more and more of a fixture gradually phasing out Klose and Boateng has joined Bayern.
6 seems to be a magical recurring number here by the way.
The stand-out exceptions here are Brazil 1958, 1970 and 1982, Argentina 1986 and 1990 (hardly all-time great teams, but there you go), France 1998 and Brazil 2002 (also not especially great).
It's not a coincidence that the standard of international football has collapsed over the past decade when most national teams consist of an amalgam of seperate club players. Even the Brazilians can't get away with it anymore.
Are all these teams' and players' achievements any less great because they had the advantage of being built around a core of same club players? I think not.