The aim of this thesis is to determine the credibility of information related to the fitness development of tennis players on social media. In the first phase of the research, 5 profiles were selected that meet the following criteria: a) profiles are publishing professional information related to fitness training of tennis players, b) profiles have a minimum of 2000 followers and c) profiles are publishing information in English. After selecting 151 videos, we created a jury consisting of 3 experts with many years of scientific and professional experience in the field of tennis and each of them evaluated the credibility of the collected material based on the following criteria: 1) Information based on scientific knowledge, 2) Practical applicability of information, 3) Demonstration quality of the presented exercises. For each variable, the experts expressed their degree of agreement on a five-point Likert scale with number one denoting complete disagreement and number five complete agreement. The results showed that the mean score of all criteria together was 3.03, with the criterion Information based on scientific knowledge receiving a mean score of 3.16, the criterion Practical applicability of information 3.03 and the criterion Demonstration quality of the presented exercises 2.89. According to the above assessments, it can be concluded that the evaluated videos are quite inaccurate and poorly verified and, as such, are not a reliable source and selection for the purpose of fitness progress of tennis players.