Mats Hummels will help to remedy a lack of quality that hampered Borussia Dortmund in the Bundesliga last season, according to team-mate Marco Reus.
Experienced defender Hummels returned to Signal Iduna Park for a second spell in June, making a €30.5million switch from Bayern Munich just three years after leaving Dortmund.
In the years without Hummels, Dortmund finished third, fourth and second in the Bundesliga while Bayern clinched consecutive titles, but the gap between the two sides was just two points at the end of a tense 2018-19 campaign.
Reus, who played alongside Hummels for four seasons at club level and for eight years in the national team, said his return could make the difference as Lucien Favre's men go in search of their first title since 2012.
"He [Hummels] brings quality," Reus told reporters. "That's most important. We were missing that last year.
"Of course, we had positive developments last season. Nobody expected that. But if we want to win the Bundesliga and advance further in Europe, we need good players.
"We found that in Mats and the other players we got."
Dortmund have also added Thorgan Hazard, Nico Schulz and Julian Brandt to Favre's squad, along with the permanent signing of last season's loan star Paco Alcacer, as they prepare to compete for honours in a division that Reus claims is shaping up to be stronger than it was last term.
With Julian Nagelsmann taking over as head coach of RB Leipzig and Bayern splashing out €115m on Lucas Hernandez and Benjamin Pavard following the departures of Arjen Robben and Franck Ribery, Reus is bracing himself for stiff competition.
"What happens with Bayern is nothing I can control," said Reus.
"I think even if they didn't buy new players they would have a strong team. They won the Bundesliga seven times in a row - that says everything.
"True, they lost some very good players who ended their careers, but we will see how the season goes.
"I hope it will be an exciting season and we cannot forget the other teams. Leipzig, with a new coach and new players, were very strong in the second part of the season.
"So, this could be between two, three, maybe even four teams until the end."