Robert Lewandowski is a "complete" striker, according to Jan Kirchhoff, who says that defenders are never left with any "advantage" against his former Bayern Munich team-mate.
Lewandowski emerged as one of the most prolific centre-forwards in Europe during a four-year spell at Borussia Dortmund, before joining their arch-rivals on a free transfer in the summer of 2014.
The 31-year-old has since scored a staggering 229 goals in 273 matches for Bayern, while helping the club win five successive Bundesliga titles.
Bayern have continued to rely heavily on the Poland international throughout the 2019-20 campaign, which has been arguably his best season yet at Allianz Arena.
Lewandowski found the net 39 times in 33 outings before Bayern's progress was halted by the coronavirus outbreak, with all major leagues in Europe forced to shut up shop amid new government rules regarding social distancing.
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Germany looks set to be the first to get back underway following the crisis, with Bayern scheduled to return to action on Sunday away at Union Berlin.
Hansi Flick's side are on course to win an unprecedented treble, thanks in no small part to Lewandowski, who has shown no signs of slowing down despite approaching the latter stages of his career.
Kirchhoff recalls being in awe of the former Dortmund star while he was on Bayern's books, and says his "unpredictable" approach in the final third made him a nightmare to play against in training during Pep Guardiola's time as coach.
The German centre-back told Goal and SPOX: "Pep wanted the number nine to fall back into midfield and play a lot. The striker should always ask central defenders whether they push forward or stay on the line.
"And in this regard - if we would be talking about my toughest opponent in terms of pure quality - Robert Lewandowski is just one number better [than Mario Mandzukic].
"Robert is fast, agile, physically and technically good, can drop and has a great finish. You simply have no advantage against him. Robert is simply complete and therefore unpredictable."
Kirchhoff went on to describe Mario Mandzukic as the most physically intimidating player he worked alongside at Bayern, while revealing that even Guardiola asked the Croatian to tone down his aggression on the training pitch.
He said: "Training against Mario meant pain. He was always looking for physical contact and tried to block every long ball. Mario often ran into the back of the defenders and sometimes jumped into the back of the defenders when the balls were in the air. Even in training, he couldn't stand losing.
"As a direct opponent of Mario, it was incredibly difficult to train well. He physically punished you.
"I had a lot of respect for him and his aggressiveness and quality as a young player at the time. I always tried to stand up to it, but I didn't want to get involved in a duel. I still remember that Pep Guardiola also said to Mario: 'Maybe you can shift down a gear and play less aggressively'."