The Arsenal fullback has returned to his old club on-loan to the end of this season.
Riether told Sport1: "Sead is good for us in all areas. Seo lives for Schalke.
"He talks a lot to the boys and asks a lot of himself and them. He is a very important component for us in the fight to stay in the league."
Kolasinac has a contract with Arsenal to 2022.