In September 2019 he signed on loan for German club 1. FC Nürnberg II.[5] In August 2020 he moved on loan to AC Horsens.[6] In June 2021, Tengstedt signed a permanent deal with the club.[7] On 1 August 2022, Tengstedt signed for Norwegian club Rosenborg.[8]
After scoring 15 goals and providing 7 assists in 14 league matches for Rosenborg, Tengstedt was sold to Portuguese club Benfica in January 2023, signing a contract until 2028.[9][10]
He made his debut for the club on 12 March, coming on as a substitute in extra-time of a 3–0 victory away at Marítimo, in the Primeira Liga.[11] Tengstedt scored his first goal for Benfica on 19 August 2023, in a league match at Estádio da Luz against Estrela da Amadora; one minute after coming off the bench to replace Arthur Cabral, with the game tied 0–0, he scored the opener, paving the way for a 2–0 victory for Benfica.[12] A month later, on 20 September, Tengstedt made his UEFA Champions League debut, coming on as a substitute for the final minutes of a 2–0 home loss to Red Bull Salzburg, in the competition's group stage.[13] On 12 November, he scored the 97th minute winner in a 2–1 league victory at home to local rivalsSporting CP.[14] On 29 November, Tengstedt made three assists, all to João Mário, in a 3–3 Champions League group stage draw at home to Inter Milan.[15] On 17 December, he scored the only goal of the match in a 1–0 league victory away at Braga.[16]
^Gomes, Rui Miguel (12 March 2023). "Classe pura sobre o relvado!" [Pure class over the pitch!] (in European Portuguese). SL Benfica. Retrieved 30 September 2023.
^Gomes, Rui Miguel (21 September 2023). "Bravos a bater de frente contra a infelicidade" [Braves hitting head on against misfortune] (in European Portuguese). SL Benfica. Retrieved 30 September 2023.