Rosenborg, keeping him until 2020. He then helped the club beat Linfield, BATE and Maribor to progress through on three UEFA Champions League rounds. However, Rosenborg was eliminated in the UEFA Champions League qualifying round after losing 3–1 on aggregate. He scored his third goal of the season, in a 3–2 win against Bodø/Glimt on 10 October 2019. However, throughout 2019 season, the club were unsuccessful to defending their league title after surrendering the title to Molde. Despite suffering from injuries later in the 2019 season, Reginiussen went on to make thirty–eight appearances and scoring four times in all competitions. However, the start of the 2020 season was pushed back to June due to the pandemic. Reginiussen were among Rosenborg players to agreeing to take a pay cut as a result of the pandemic. Following the departure of Jensen, he resumed his role as the club's captain. Reginiussen captained his first match in almost a year, starting the whole game and helping Rosenborg keep a clean sheet, in a 0–0 draw against Kristiansund in the opening game of the season. Since the start of the 2020 season, he continued to establish himself in centre–back position, forming a partnership with Hovland and Eyjólfsson. Reginiussen helped the club keep three clean sheets in three matches between 5 July 2020 and 16 July 2020. A month later on 27 August 2020, he scored his first goal of the season, scoring from a header, in a 4–2 win against Breiðablik to advance to the next round of the UEFA Europa League. Reginiussen then scored his second goal of the season, once again scoring from a header, in a 3–1 win against Molde on 13 December 2020, in what turned out to be his last appearances for Rosenborg. Despite missing a total of four matches during the 2020 season, he went on to make twenty–nine appearances and scoring two times in all competitions. At the end of the 2020 season, it was announced on 18 December 2020 that Reginiussen and Rosenborg parted ways after eight years at Rosenborg. Reginiussen previously stated in an interview earlier this year that this would be his last season with the club. Following his release by Rosenborg, he was linked with a move to Ranheim and has ruled out from retiring. FC St. Pauli On 25 January 2021, Reginiussen returned to Germany, where he signed with 2. Bundesliga team, FC