A promising talent in Rugby union, he won the Frantz-Reichel Cup in 1938 but missed out on playing in the final of the French Championship the following year, despite his team qualifying.

He missed the 1943–1944 season, during which his club won the French Championship title with his teammates Joseph Crespo, Puig-Aubert, Frédéric Trescazes, and Lucien Barris.

[5] Upon his return to France in 1945, a friendly Rugby union match involving USA Perpignan and Castres Olympique changed Henri Riu's life.

The club had won the French Championship in 1939 with players like René Arotça, Jean Dauger, and Max Rousié, but the war and the Vichy regime had halted the competition.

[6][7] He settled in the Roanne area and joined a team where many Catalans, including Crespo, were already playing, under the guidance of coach Jean Duhau, a former French international in both Rugby union and league before the war.

The club came close to reaching the finals of both the Championship and the French Cup but was defeated in the semi-finals on both occasions, losing to the eventual champions, AS Carcassonne (15–3),[8] and XIII Catalan (8–7).

Roanne's coach, Jean Duhau, who was called upon to build RC Marseille under Paul Ricard, was replaced by former international player Robert Samatan.

However, Riu's name continued to be mentioned in squad discussions, and he eventually earned his first cap in March 1948,[14] remaining the first replacement for the forward lines.

Roanne delivered a flawless performance against a lackluster Carcassonne side, securing a 19–0 victory with thirteen points from Gaston Comes, who was named the man of the match.

Brousse's departure led Samatan to move Henri Riu to the second row, where his understanding of the game could compensate for the physical play without disrupting the team's performance.

[17] While Roanne aimed for another championship with AS Carcassonne and RC Marseille as main competitors, Riu's name circulated within the French national team, although he was not called up for the European Cup.

However, he seemed to have a good chance for the New Zealand tour of Europe that winter, alongside Lucien Barris, Joseph Crespo, Puig-Aubert, and Paul Dejean,[18] especially considering his strong performances in the Championship with his club.

[27] The 1948–1949 season for RC Roanne was marked by difficulties due to injuries plaguing the squad, including key players like Robert Dauger, René Duffort, and Roger Pouy, forcing coach Robert Samatan to constantly adjust his starting thirteen,[28] coupled with the departure of quality players such as Raymond Contrastin, Henri Gibert, and Lucien Barris.

[29] Despite the challenges, H. Riu retained his place in the Roanne squad, where he performed well at the beginning of the season and was under consideration for French national team call-ups in the fall of 1948.

It was noted by the sports press that while his performances for his club under R. Samatan's guidance demonstrated authority and initiative, they were not replicated in the French team due to tactical differences where he was less supported in his movements.

H. Riu was present in the front row for the Coupe de France semi-final at the Parc des Princes in Paris against AS Carcassonne, lost 21–6 in a match where Roanne had to play with ten men at times due to injuries to Jean Barreteau and Rodeila, among others.

The Marseille team, in dazzling form and buoyed by the partnership of Jean Dop and Paul Césard, handed Roanne a 22–0 defeat, marking their worst performance of the season and concluding their campaign with two semi-final eliminations.

This transfer was finalized in September 1949, with many players, including Henri Riu, following suit, along with Jean Audoubert, René Duffort, Pierre Taillantou, Joseph Crespo, and their coach Robert Samatan.

[40] The early matches dispelled any doubts about this Lyon team, which quickly positioned itself at the top of the Championship standings and was potentially recognized as a candidate for national titles.

[45] Henri Riu did not participate in the Coupe de France final against XIII Catalan, held in Perpignan, which they lost 12–5, concluding the 1949–1950 season without a title.

[47] At the age of 30, Henri Riu started this new season on the banks of the Rhône with U.S. Lyon-Villeurbanne, which claimed its status as a contender for national titles, strengthened by the arrivals of players like Roger Rey or Hugues Baldassin, among others.

The following week, in the Coupe de France semi-final, the two teams met again for a rematch, despite Carrère's absence from the Catalan side, replaced by Ascola.