Hamburger SV
For the 2009–10 season, Mickel moved to Hamburger SV. There, he signed a professional contract until 30 June 2012, which was extended in October 2011 by one year, to 2013.[4] During his time in Hamburg, Mickel was continuously number two or three in the goalkeeper depth chart. In three and a half years, Frank Rost, Jaroslav Drobný and René Adler were preferred to him. He therefore mainly appeared for the second team, Hamburger SV II, in the fourth-tier Regionalliga Nord.
Return to Hamburger SV
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.[7] After the trial practice, Mickel was signed to the second team. He signed a contract until the end of the 2015–16 Regionalliga season.[8] On 14 May 2016, Mickel made his Bundesliga debut for HSV in a 3–1 win over FC Augsburg on the last match-day, which was made possible by injuries to René Adler and Andreas Hirzel.[9] Mickel made 20 appearances in the Regionalliga for HSV II.
In the 2016–17 season, Mickel beat out Hirzel for the position as third goalkeeper of the first team. He also made his second Bundesliga appearance for HSV in Augsburg when FC Augsburg beat HSV 4–0 on 30 April 2017.[10] After the end of the season, Mickel extended his expiring contract with HSV until 2019.[11] For the second team, Mickel was utilised in 17 games.
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.[12] During the season, Mickel made five times for the second team.
Before the 2018–19 season, in which HSV played in the 2. Bundesliga for the first time after relegation, Mickel extended his contract until 30 June 2021.[13] After Mathenia had left for newly promoted Bundesliga side 1. 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. Bundesliga after Pollersbeck fell out with an injury. He also made one appearance in the Regionalliga.
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. Mickel was preferred as the backup goalkeeper over Pollersbeck.[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.[15] From the following round, however, Heuer Fernandes was named backup to Pollersbeck with Mickel demoted to third option.[16] While Mickel did not play a competitive game for the first team, he made two appearances in the Regionalliga for the second team.
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.[17]