Bundesliga bottom club Schalke completed an extraordinary piece of business after the transfer deadline by signing World Cup winner Shkodran Mustafi as Ozan Kabak moved on loan to Liverpool, who have an option to buy the player.
Kabak will strengthen the Premier League champions given their defence has suffered from injuries while Mustafi, who left his Arsenal contract to join Schalke to the end of the season, will fight to keep the Royal Blues in the top-flight.
Mustafi won the World Cup with Germany in 2014 but has fallen out of favour with Arsenal, playing only three times this season.
"This change must be viewed in two perspectives: economically the transfer of Ozan Kabak makes a lot of sense for Schalke ... and we're convinced that with Shkodran Mustafi we could bring in a good centre back to fill the sporting gap Ozan leaves," said Schalke director for sport Jochen Schneider.
