AC Milan midfielder Kevin-Prince Boateng says Jurgen Klopp "is like a friend" to him and there is a possibility that he will play for Borussia Dortmund again in the future.
The Ghana international, who came out of national retirement in June, played under the German trainer whilst on loan at Signal Iduna Park in 2009 from Tottenham.
Boateng, whose deal with the San Siro outfit expires in June 2015, has suggested he could imagine returning to Germany's top flight in the future, and that he still keeps in regular contact with Klopp.
"Bundesliga is always interesting to me," he told Eurosport.
"However, at the moment, I'm still wearing the red-and-black jersey of Milan.
"At the moment Klopp is still busy with his pre-season preparations, so he doesn't have much time. We both have a lot of things to do.
"But we chat regularly. And that won't change, as he is like a friend of mine."
The 26-year-old praised die Schwarzgelben and treble-winners Bayern Munich for their impressive display in the Champions League last term, and also in last month's DFL-Supercup final where Dortmund ran out 4-2 winners in Pep Guardiola's debut as Bayern coach.
"They made it to the Champions League final - so of course they are the benchmark at the moment," he added.
"You could see it again during the Super Cup clash at which pace they are playing football, it's gigantic!
"Even Barcelona and Real Madrid had to upgrade."