Due to the small number of official matches at the national level, the club played numerous international friendlies, which caused a stir in the press and among fans. In 1923, Slavia played extensively against powerful German, Austrian, and Spanish clubs. However, the young Soltis didn't always fit into the starting eleven or have a defined position on the field. The undisputed core players were forwards Jan Vaník and Rudolf Sloup, while Karel Kužel and Josef Kratochvil played on the wings. Jindřich competed for the fifth striker spot with his friend Čapek or substituted for one of the aforementioned players.

In 1925, the country's first professional championship was held in Czechoslovakia. Ten teams played in a single-round tournament, although a full tournament was originally planned, but another change in the regulations occurred with the transition to the autumn-spring system. The title fight was traditionally led by Slavia and Sparta. In the head-to-head match at the end of the tournament, Sparta won 2:0 and caught up with their opponent on lost points. However, Slavia retained a significant advantage on goal difference. Most of the championship matches were played until June, but the announcement of the champion had to be postponed until November, when Sparta played a postponed match against Vršovice. By that time, the new championship was already in full swing. In the postponed match, Sparta only managed to win by a double-digit score. They managed to win with a modest score of 3:2, making Slavia the first champion of the Czechoslovak professional league [ 16 ]. Soltys played seven of nine matches as a right winger. He scored only one goal against Meteor VIII (5-0). The five main forwards of the champion team were: Soltys - Slope-Staple - Vanik - Silny - Kratochvil

In the following championship, 1925-26, Jindřich scored significantly more. He scored 25 goals in 20 matches, allowing him to take second place on the season's top scorers list after Sparta's Jan Dvoráček, who scored 32 goals [18]. Rudolf Sloup left Slavia, freeing up the right-sided midfield position for Soltys. Also at the beginning of the season, legendary goalscorer Jan Vaník finished his performances. Josef Silny moved to the center forward position, and the young Antonín Puč played on the left.