During the winter break of the 2012–13 season, Mickel moved to league rivals SpVgg Greuther Fürth six months before the expiration of his contract.

Mickel made his professional debut on the 8th match-day of the 2013–14 season when he was substituted on for the injured Wolfgang Hesl in the 77th minute of the match against 1860 Munich.

At the beginning of the 2015–16 season, Mickel completed a trial practice session at his former club Hamburger SV as part of the team's training camp in Graubünden in order to recommend himself for a permanent commitment.

Towards the end of the first half of the 2017–18 season, Mickel was temporarily promoted to backup goalkeeper behind Christian Mathenia by head coach Markus Gisdol as the replacement of Julian Pollersbeck because of his good performances at practice.

FC Nürnberg, Mathenia was now the backup to new first keeper Pollersbeck ahead of Morten Behrens, who had been promoted from the second team to the professional squad.

Mickel appeared for HSV in the DFB Cup first round matchup under new head coach Christian Titz against Oberliga club TuS Erndtebrück and under his successor Hannes Wolf he played 3 matches in the 2.

A new goalkeeper, Daniel Heuer Fernandes, was ahead of the 2019–20 season and subsequently named the starter by the new head coach Dieter Hecking.

[14] He also remained the backup when Heuer Fernandes was replaced by Pollersbeck on 31 May 2020, in a league match against SV Wehen Wiesbaden.

For the 2020–21 season, Mickel was named backup to new signing Sven Ulreich by new head coach Daniel Thioune, with Heuer Fernandes completing the goalkeeping trio as third option in the HSV goal.