Early career Zaleski started his MMA career on November 8, 2009, and he fought for many promoters notably
Jungle Fight, Smash and Amazon Fight in Brazil. He was the former Jungle Fight welterweight champion and he built a record of 14–4 with 13 finishes and 1 decision prior joining UFC.
Ultimate Fighting Championship Zaleski made his promotional debut on May 30, 2015, at
UFC Fight Night: Condit vs. Alves against
Nicolas Dalby. Zaleski outstruck Dalby as he landed 16 more significant strikes, but judges handed the victory via split decision to Dalby as he successfully took Zaleski down six times. He faced
Omari Akhmedov on his next fight at
UFC on Fox: Teixeira vs. Evans on April 16, 2016. The fight earned him his first
Fight of the Night bonus award. On October 1, 2016, Zaleski returned to face
Keita Nakamura at
UFC Fight Night: Lineker vs. Dodson. After three rounds of fighting, he won the fight with a unanimous decision with the score board of (29–28, 29–28, 29–28). Zaleski faced
Lyman Good, former
Bellator and CFFC champion, on July 22, 2017, at
UFC on Fox: Weidman vs. Gastelum. He won the back-and-forth fight by split decision. The fight also earned him his second
Fight of the Night bonus award. Zaleski faced
Max Griffin on October 28, 2017, at
UFC Fight Night: Brunson vs. Machida. He won the fight with a unanimous decision. The win also earned him his third
Fight of the Night bonus award. Zaleski was expected to face
Jack Marshman on March 17, 2018, at
UFC Fight Night 127. However, on February 19, 2018, Zaleski announced that he is pulling out of the fight because of a knee injury. He was replaced by
Brad Scott Zaleski faced
Sean Strickland on May 12, 2018, at
UFC 224. He won the fight with a knockout in the first round. Zaleski was scheduled to meet
Belal Muhammad on September 22, 2018, at
UFC Fight Night 137. On September 14, 2018, Muhammad was pulled out of the bout and he was replaced by newcomer
Luigi Vendramini. He won the fight via knockout in round two. Zaleski was scheduled to face
Li Jingliang on November 25, 2018, at
UFC Fight Night 141. However on October 27, 2018, reports were made that Zaleski withdrew from the bout due to a partial ligament tear in his right knee. Zaleski faced
Curtis Millender on March 9, 2019, at
UFC Fight Night 146. He won the fight through submission in the first round. Zaleski was expected to face
Neil Magny on May 18, 2019, at
UFC Fight Night 151. However, on March 28, 2019, dos Santos announced that he had not been contacted by the UFC about the match. A pairing with
Li Jingliang was rescheduled and took place on August 31, 2019, at
UFC Fight Night 157. He lost the fight due to a technical knockout in round three. As the last fight of his prevailing contract, Zaleski faced
Alexey Kunchenko on March 14, 2020, at
UFC Fight Night 170. He won the fight with a unanimous decision. As the first fight of his new, four-fight contract, Zaleski faced
Muslim Salikhov on July 11, 2020, at
UFC 251. He lost the fight with a split decision. Zaleski was expected to face promotional newcomer
Shavkat Rakhmonov on October 24, 2020 at
UFC 254. However, Zaleski pulled out in late September due to a knee injury that required surgery. Zaleski faced promotional newcomer
Benoît Saint-Denis on October 30, 2021, at
UFC 267. After nearly finishing Saint-Denis in round two, he won the bout with a unanimous decision. Zaleski was scheduled to face
Mounir Lazzez on April 16, 2022, at
UFC on ESPN 34. However, Zaleski dos Santos withdrew the week of the fight for personal reasons and was replaced by Ange Loosa. On September 22, 2022, it was announced that
USADA suspended Zaleski for 1 year after testing positive for
ostarine in an out-of-competition test on March 14, 2022. Zaleski and his team contended that the test was due to a contaminated supplement. He is eligible to return on March 14, 2023. Zaleski faced
Abubakar Nurmagomedov June 3, 2023, at
UFC on ESPN 46. He won the fight through a split decision. Zaleski faced
Rinat Fakhretdinov on November 4, 2023, at
UFC Fight Night 231. The bout ended in a majority draw. Zaleski faced
Randy Brown on June 1, 2024, at
UFC 302. He lost the fight by unanimous decision. Zaleski was scheduled to face
Nicolas Dalby in a rematch on November 9, 2024 at
UFC Fight Night 247. However, Dalby withdrew from the fight for unknown reasons and was replaced by promotional newcomer Zach Scroggin. At the weigh-ins, Scroggin weighed in at 174 pounds, three pounds over the welterweight non-title fight limit. The bout proceeded at catchweight and Scroggins was fined a percentage of his purse, which went to Zaleski. Zaleski won the fight by technical knockout early in the first round. Zaleski faced
Chidi Njokuani on March 15, 2025, at
UFC Fight Night 254. At the weigh-ins, Njokuani weighed in at 172.5 pounds, one and a quarter pounds over the welterweight non-title fight limit. The bout proceeded at catchweight and Njokuani was fined 20 percent of his purse which went to Zaleski dos Santos. Zaleski lost the fight by technical knockout via a knee and elbows in the second round. Zaleski faced
Neil Magny on August 2, 2025 at
UFC on ESPN 71. Zaleski lost the fight by technical knockout at the end of the second round. On December 22, 2025, it was reported that Zaleski was released by the UFC. == Championships and accomplishments ==