Mario Gotze returns to Dortmund training

Alongside fellow new signings Andre Schurrle and Raphael Guerreiro, Gotze was put through his paces with a series of fitness tests at Bochum University by Borussia's backroom staff.

The trio joined a group of six players returning from their holidays after international duty including Poland's Lukasz Piszczek, Julian Weigl and South Korean Park Joo-Ho.

"Finally, let's go," wrote Goezte on his Twitter account under a picture of the Germany star on a treadmill.

His first training session with the full Dortmund squad takes place on Wednesday with Borussia to host his former club Bayern for the German Super Cup on August 14.

Gotze left Dortmund for arch-rivals Bayern at the end of the 2012/13 season and lived up to his billing as a rising Germany star by volleying home Schurrle's cross in extra-time for the winning goal in the 2014 World Cup final against Argentina.

But he has endured three unproductive years at Bayern, mainly spent on the bench or injured, having failed to impress coach Pep Guardiola or hold down a first-team place, despite collecting three back-to-back Bundesliga winner's medals. 

Having paid 37 million euros for Goetze in 2013, Bayern sold him back to Dortmund for €26 million last month and the 24-year-old has plenty to prove again in the black and yellow shirt.

Likewise, Schuerrle needs some good performances after 18 months at Wolfsburg, having failed to impress on his return from an unsuccessful spell at Chelsea, and has been signed by Dortmund for around 30 million euros.

"At the end of the day, it's primarily about one thing for both of them: performance, performance, performance," Dortmund's director of sport Michael Zorc told Kicker magazine.

"Neither Mario nor Andre have had top years behind them and they have not taken the easy path.

"For them, it's clear that they will be scrutinised in the public eye".

Having come up through Dortmund's academy, only to turn his back to join Bayern, Goetze could encounter some hostility from Dortmund's fans, at least initially.

"If some people feel compelled to boo him, they should do it," Dortmund CEO Hans-Joachim Watzke said on the subject of Gotze's return, with their first game of the league season at home to Mainz on August 27.

"We have a democracy. But I'll react like an allergy when someone is personally insulted.

"That doesn't do anyone any good".

Dortmund coach Thomas Tuchel says his goal is to see Goetze 'laugh again' with good performances, after scowling his way through the last few months in Munich.

Tuchel has also added Portugal left-back Guerreiro, midfielder Sebastian Rode, former Barcelona defender Marc Bartra and exciting teenage striker Ousmane Dembele.

Schurrle is a direct replacement for Henrikh Mkhitaryan, who has left to join Manchester United, as Dortmund try to end Bayern's four-year stranglehold on the Bundesliga title with Carlo Ancelotti now in charge of the Munich giants.