Two of football's most intriguing coaching minds finally meet on the field on Sunday when Pep Guardiola's Barcelona takes on Marcelo Bielsa's Athletic Bilbao.
The two coaches face off for the first time since Bielsa took over Bilbao this season, and the Basque club has been steadily improving following a poor start.
Guardiola visited the former Argentina and Chile coach to pick his mind over tactics and philosophy after retiring from football in 2005. The Catalan coach then embarked on his coaching career, which stared with Barcelona's reserve squad before taking over the senior team to start the 2008-09 season.
Barcelona has won 12 trophies since Guardiola took charge, with the 40-year-old winning 144 of his 200 games, with just 17 losses.
"(Sunday) will be another good test," Guardiola said after his team beat Viktoria Plzen 4-0 in the Champions League on Tuesday to remain undefeated in 17 games to start the season.
Messi scored a hat trick for the second consecutive game in Prague - his fourth of the season - to take his goal tally to 22 from 17 games. The Argentina forward is only 33 goals away from Cesar Rodriguez's club record 235 goals.
"Messi will pass Cesar as the club's all-time leading scorer, it's already a done deal, and I don't discount him doing it this season," said Guardiola, who has seen Messi score 160 of his goals since he took over. "And he's only 24 years old, that says it all."
Bilbao is unbeaten in eight games in all competitions and has moved up to ninth, despite Bielsa's reign starting with three losses in his first six matches.
"We try to treat every game with the same importance," Bielsa said. "Whether it goes our way or not we'll see, but the idea out of the start is always the same."
Bilbao has a number of injury worries going into the match after 10 players were diagnosed with problems this week. And it also had a Europa League match at Salzburg to get through on Thursday.
Bilbao, which fields only Basque-born players, is one of only three clubs to never have dropped out of the first division - the other two being Barcelona and Real Madrid.