Matches held in hot weather represent a great challenge for the body in terms of regulating body temperature. It is well known that in conditions of high temperatures, athletes’ sweat rates can be high, while increased loss of water and electrolytes can negatively affect sports performance, as well as the health of players. Dehydration leads to an increased strain on the cardiovascular system, muscle fatigue, reduced ability to recover, which in turn results in a decrease in speed, endurance and focus of athletes. The issue of fluid loss in athletes has sparked some interest, but little research has been conducted during a football match in competitive conditions. The aim of this research was to assess the hydration status of football players before and after a football match, fluid loss through sweat and the amount of fluid ingested during a football match at high temperatures. The research was done on a sample of 20 senior semi-professional players who played two friendly matches: the first one at 29.4°C, with 75 % air humidity, and the second one at 23.4°C, with 62 % air humidity. The results of the research revealed that the players’ average body mass loss during a match was -1.06 ± 0.88 kg, and it varied between -2.45 kg and 0.8 kg. Dehydration averaged 1.4 ± 1.19 %. 30% of players displayed dehydration greater than 2 % of their body mass, which is considered the limit after which sports performance decrease due to dehydration The average sweat loss amounted to 650 ml, and the sweating rate was 600 ml/h. By monitoring the weight gravity of urine, it was determined that 35 % of the players, 7 out of 20 showed up to the match dehydrated. The difference between the data was statistically significant: the specific weight of urine before the match was 1.020, and 1.025 after the match. 13 out of 20 players were dehydrated after the match, i.e., 65 % of the players. We can conclude from the obtained results that it is necessary to educate players and coaches about the importance of hydration with an emphasis on the individual needs of each athlete, since some of the players came to the match dehydrated, and after the match most of them were dehydrated.