Early career In his youth, Heyer played for 1. FCR Bramsche, TSV Wallenhorst and
VfL Osnabrück. With the latter, he progressed through the U17 and U19 sides and appeared in the
Under 17 and
Under 17 Bundesliga. In September 2013, Heyer made his first appearance for the second-team,
VfL Osnabrück II, in the fifth-tier
Oberliga Niedersachsen.
Sportfreunde Lotte Ahead of the 2014–15 season, in May 2014, Heyer moved from the Osnabrück U19 team to
Sportfreunde Lotte in the fourth-tier
Regionalliga West. After not being utilised under head coach
Michael Boris, he began making an impact under his successor,
Ismail Atalan, at the end of the season, making four appearances, of which two were starts, and he scored a goal. In the 2015–16 season, Heyer established himself as a regular starter under Atalan in the second half of the season. He contributed with three goals in 26 appearances, of which 18 were in the starting lineup, with the team finishing with the Regionalliga West championship at the end of the season. In the 2016–17 season, Heyer, who from then increasingly played in central defense, was again part of the regular starting lineup and made 33 appearances in the 3. Liga, with 23 of them being as a starter, in which he scored two goals.
Oscar Corrochano took over as head coach ahead of the 2017–18 season, as Atalan had moved to
VfL Bochum. Under Corrochano and his successor
Andreas Golombek, Heyer was again mainly used in the defensive midfield and scored three goals in 34 appearances.
Hallescher FC In the summer of 2018, Heyer signed a one-year contract with 3. Liga club
Hallescher FC on a free transfer. Under head coach
Torsten Ziegner he almost exclusively played in central defense and made 36 appearances during the season, in which he scored 3 goals. In the sports magazine
kicker, Heyer was subsequently one of the top ranked central defenders in the 3. Liga.
VfL Osnabrück In May 2019, Heyer signed for
VfL Osnabrück on a two-year deal, after they had reached promotion to the
2. Bundesliga. Under head coach
Daniel Thioune, Heyer was one of the regulars right from the start. He played mainly in central defense, but was also utilised in defensive midfield and as a right-back. In 33 2. Bundesliga appearances, Heyer scored six goals. In
kicker he was rated as the third best central defender of the league after the season. VfL Osnabrück finished 13th in the league at the end of the season.
Hamburger SV On 17 September 2020, one day before the first matchday of the 2020–21 season, Heyer signed a three-year contract with
Hamburger SV in the 2. Bundesliga. The move reunited him with his former Osnabrück coach Daniel Thioune. He would initially feature as a
centre-back alongside
Stephan Ambrosius, but had to replace the injured
left-back and captain
Tim Leibold on the third matchday. Over the course of the first half of the season, Heyer oscillated between
defensive midfield and centre-back when Thioune would utilise a formation with three at the back. From the 14th matchday on, Heyer was used in a
4–3–3 system as the defensive midfielder. Manager
Tim Walter took over HSV for the
2021–22 season. After Heyer was initially used in the 4–3–3 formation as a
central midfielder, he mainly played as the team's
right-back later on. In this position he replaced
Jan Gyamerah, who had been a regular starter after the injury of
Josha Vagnoman until that point. In April 2022, Heyer extended his contract until 2026.
Fortuna Düsseldorf On 28 January 2025, Heyer moved to
Fortuna Düsseldorf. ==Career statistics==