Kajzer began his career with ROW Rybnik, making his senior debut in 2012. In the 2012–13 season, he helped the team achieve promotion to I liga. Kajzer made a total of 103 league appearances across five seasons with the club, keeping 28 clean sheets.
Botev Plovdiv
On 12 June 2017, after a successful trial period, Kajzer signed a two-year contract with Bulgarian club Botev Plovdiv. He made his debut in the final for the Supercup of Bulgaria against the champion Ludogorets. The match was decided on penalties with Kajzer saving the first penalty shoot taken by the star of LudogoretsMarcelinho. Subsequently, the saved penalty was decisive for the triumph of Botev Plovdiv, and Kajzer became one of the heroes for Botev Plovdiv.[2]
On 6 April 2018, Kajzer was included in the starting line-up and kept a clean sheet during the 1–0 win in the derby match against Levski Sofia.[3]
On 29 April, Kajzer saved a penalty in the last minutes for the 2–1 home win over CSKA Sofia.[4] His performance in the game was selected for save of the week.[5]
On April 24, 2019, Botev Plovdiv faces CSKA Sofia in a rematch of the semi-final of the Bulgarian Cup tournament. The match ends 3:3 at the "Bulgarian Army" stadium and sends Botev Plovdiv to the final. Kajzer plays a phenomenal game and saves a lot of chances in front of his goal and he is once again one of the heroes for the Botev Plovdiv.
With his great performances in Botev Plovdiv he became one of the favourite players of the fans and the Bultras.
Arka Gdynia
After spending the 2019–20 season as a back-up with Śląsk Wrocław, making only one cup appearance, on 28 July 2020 he joined Arka Gdynia.[6]
Return to Botev Plovdiv
On 27 June 2023, Kajzer returned to Botev Plovdiv, signing a two-year contract.[7] He made a single Bulgarian Cup appearance that season, keeping a clean sheet in a 0–3 first round win over Strumska Slava on 8 November 2023.[8] Botev went on to win the competition.[9]