2009-10: Alexander Kadeykin skated for the lower division Crystall 1993-born team in his hometown of Elektrostal. In 24 Moscow region games he scored 32 goals with 32 assists and 30 penalty minutes. Kadeyki was selected by Atlant Mytishchi
2010-11: Kadeykin moved from Elektrostal to Mytischi to play for the Atlanty club in the Russia U22 league, the MHL. He scored 9 goals with 20 assists and was +6 with 42 penalty minutes in 48 regular season games. Kadeykin scored 1 goal with 1 assist and was minus-3 with 2 penalty minutes in six playoff games.
2011-12: Kadeykin was the second-leading scorer for Atlanty Mytischi behind Sergei Shmelev in his second season with the club. He scored 22 goals with 36 assists in 60 games and was +29 with 20 penalty minutes. Atlanty reached the MHL playoff semifinals before falling to Red Army and in 12 playoff games Kadeykin scored 7 goals with 9 assists and was +11 with 22 penalty minutes.
2012-13: Kadeykin made his KHL debut in February after skating with the Atlanty Mytischi junior team in the MHL; missing time at the start of the year due to a serious knee injury. He had no points nor penalties in two regular season KHL games for Atlant Mystishchi and was minus-1 with no points nor penalties, averaging 2:39 minutes of ice time in two playoff games. He scored 14 goals with 29 assists and was +32 with 4 penalty minutes in 26 regular season games for Atlanty and scored 4 goals with 7 assists, finishing +3 with 6 penalty minutes in eight MHL playoff games.
2013-14: Kadeykin was the leading scorer for Atlant Mystischi as a 20-year-old skating on a line with former NHLer Evgeny Artyukhin and fellow KHL rookie Sergei Shmelev. He scored 8 goals with 15 assists and was +17 with 24 penalty minutes in 54 regular season games. Atlant missed the playoffs after finishing fourth in the Tarasov Division. In his third year of draft eligibility Kadeykin was selected by Detroit in the seventh round (201st overall) in the 2014 NHL Draft.
2014-15: Kadeykin returned to Atlant Mystischi, registering one assist in nine games, and was traded to SKA St. Petersburg in exchange for Anton Malyshev at the end of September 2014. He played 20 regular season games for SKA, scoring 4 goals with 4 assists and was +4 with 2 penalty minutes.
Kadeykin is the younger brother of one-time Devils' prospect defenseman Anton Kadeykin. The younger Kadeykin's developing two-way game attracted Detroit's attention. He is a good defender and passer with an innate sense of where to be on the ice. He needs to improve his skating and is still a work in progress in terms of consistency and positional play.