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Messi is one game away from matching Xavi as the players with the most games in Barcelona's history – 767 – ahead of Tuesday's (AEDT) LaLiga clash against Huesca.
Messi, who already holds the record for most trophies (34) and goals (658) in club history at Camp Nou, equalled Barca's all-time LaLiga appearances mark set by Xavi last month.
The Argentinian star has featured in 509 LaLiga matches, while playing 149 Champions League fixtures, 79 Copa del Rey games, 20 in the Supercopa de Espana, five in the Club World Cup and four in the UEFA Super Cup.
"Well it is an incredible number of games," Koeman said. "That also shows what Xavi did for the club, and now Messi will equal the number games of Xavi.
"It will be a great day and then the next that will be one more than Xavi achieved with Barcelona. It is incredible because that shows how important he is and was for Barcelona.
"The number of games, the number of goals, the number of hat-tricks, the number of titles.
"Let's hope that we will continue with Leo, winning titles, what he showed and what he did for this club."
The 33 year-old tops LaLiga's goalscoring charts this season with 19 as Barca looks to close within four points of leader Atletico Madrid.
Messi has been involved in five goals in two games against Huesca in LaLiga (two goals and three assists), including two goals and two assists in his only league appearance against the 'Oscenses' at Camp Nou.
Barcelona has gone 16 games without losing in LaLiga (W13 D3) – the best current unbeaten streak of any team in the five major leagues in Europe.