Kagawa left Dortmund for Old Trafford two years ago and he has scored six goals in 54 appearances for United.
However, he has started just 12 Premier League games this season amid suggestions United have struggled to get the best out of the Japan international.
The 25-year-old has been linked with a return to Dortmund and Hummels would not complain if Kagawa was re-signed by the Bundesliga club.
"We would take him with open arms, of course," he told Kicker.
"Having an offensive line with [Marco] Reus, [Henrikh] Mkhitaryan and Kagawa would certainly be stylish.
"But I would not say anything about the other great players we have playing for us. The attacking midfield is probably the best part of our team without Shinji."
Hummels is also not concerned by the impact any possible big-money signings this summer will have on the morale of Jurgen Klopp's squad.
He added: "I cannot imagine that it would be a big issue with us. In our team we are not only out for success.
"At the end of the day, everyone is responsible for their own contracts. Nobody forced us to sign them. We want to play good football.
"If we had a star attacker who earned more money than us, no one would feel bad about it."