A couple of years ago Nuri Sahin was at the centre of a loan tug-of-war between Arsenal and Liverpool, with the midfielder's services not required at Real Madrid.
He chose Liverpool but failed to shine, dominated when the club's met at Anfield by an Abou Diaby inspired Gunners outfit.
His contract was terminated early by the Reds, and he signed on loan with Dortmund, on an 18-month loan deal, which was finally made permanent this summer.
Dortmund were drawn against Arsenal for the second year in succession at the Champions League group stage a week ago, but Sahin's chances of featuring have been dealt a blow.
Borussia Dortmund confirmed on Wednesday that Sahin has undergone knee surgery.
The midfielder has a history of knee problems, and German website Sport1 estimate that the midfielder will be out for at least two months.
The 25-year-old started 34 matches for Dortmund last season, and his absence is a blow to Jurgen Klopp's squad.
There is also potential impact for Arsenal, who travel to Dortmund for their opening Champions League clash on September 16. Sahin will certainly miss that fixture.
It is also fair to estimate the star has a 50/50 chance at best of making the return fixture at The Emirates on November 26.
How much of a blow do you expect Sahin's absence to be to Dortmund?