Martinez left Barca for Al-Nassr at the start of the LaLiga season.
Reflecting on Barca's defeat at Real Madrid on Sunday, Kroos said on his podcast: "I've always said how important Iñigo Martínez (now at Al-Nassr) was to me . Of all the central defenders at Barça last season, he was the best at coming out of his own half.
"He wasn't the fastest, but he was excellent at recovering the ball and his distribution was remarkable. Against Real Madrid, his absence was felt at times, especially during Real's pressing. They didn't replace him, and his absence was felt at times, especially during Real's pressing. They didn't replace him, and his absence is felt."
Kroos continued: "In central defence, I don't understand why Eric Garcia played, given that, technically speaking, he's slightly better than (Ronald) Araújo. But Araújo has the physical strength to put more pressure on the opponents, especially when he defends so high up the pitch. He would have been the ideal player for this style of play and this opponent.
"Frankly, I don't understand it. Against (Kylian) Mbappé and Vinícius, you need someone who can keep up with their pace. Araújo is capable of that. His absence surprised me a lot."