The aims of this study were to assess the speed-power characteristics of professional futsal players pre- and post- a 9-week preseason and to explore possible relationships with internal training loads. Ten U-20 professional Brazilian futsal players performed unloaded [squat jump (SJ) and countermovement jump (CMJ)] and loaded [jump squat (JS)] jumps and a 20-m sprint test prior to and after the preseason. Weekly training loads as measured by session-rating of perceived exertion (sRPE) varied between 2179 and 5519 a.u. The magnitude based inference statistics revealed that performance in the SJ, CMJ and 20-m sprint very likely decreased (ES = -0.64, -0.49, and -0.92, respectively), while mean propulsive power in the JS likely increased (ES = 0.42) in response to the preseason. The Pearson coefficient of correlation between velocity in the 20 m sprint test and s-RPE during the first two weeks of training was 0.66 (P< 0.05), while no significant correlation was detected between total s-RPE (i.e., 9 weeks) and changes in the power-speed tests. The baseline 20 m sprint velocity was very largely and inversely (r = -0.90) correlated with the change in the 20 m sprint performance. In conclusion, futsal preseason training leads to impaired unloaded vertical jump and sprint test performance, with speed decreasing more in faster than slower players. In addition, due to the large correlation between baseline sprint ability and s-RPE, coaches are advised to assess sprinting performance at the beginning of the preseason in order to finely adjust the training stimuli to each athlete.