Hamburg SV winger Nicolai Mueller will be sidelined for about seven months and will need surgery after tearing a cruciate ligament while celebrating a goal during the side's opening Bundesliga game on Saturday.
The 29-year-old Mueller scored the only goal of the match against Augsburg but as he raced towards the corner flag to celebrate with fans he stumbled over it and fell, tearing his ligament in the process.
He tried playing on but had to be taken off.
"This diagnosis is a big shock for us all and a heavy blow for Nicolai at the start of the season," Hamburg sports director Jens Todt said on Sunday after a medical check on Mueller.
Saturday's win was the first for Hamburg at the start of the season in seven years with the former European champions having narrowly avoided relegation in three of the last four seasons.
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