Schalke coach Markus Weinzierl claims the challenge that broke the ankle of striker Breel Embolo was "stupid."
Embolo, 19, suffered the injury in a challenge with Augsburg defender Konstantinos Stafylidis early on in Saturday's 1-1 Bundesliga draw and will now not play again in 2016.
Weinzierl, who left Augsburg in the summer to take on the Schalke job, does not believe there was malice in the tackle but is certain it was avoidable.
"I know the player and I know that his thoughts were not straight -- he just sees the ball and is an aggressive player and something like this can happen," Weinzierl, who signed Stafylidis for Augsburg in August 2015, told Sky Deutschland. "I'm not saying he meant it, but it is stupid.''
Schalke's director of sport Christian Heidel also expressed disappointment at the challenge.
"It's hard for me to talk about the game at all," Heidel told kicker. "This could not be more tragic for Breel Embolo. He's been really settled in the Bundesliga in the past two games and he was also our most impressive player until the injury.''
Stafylidis made an apology on Saturday night, writing on Instagram that he is an aggressive player but that he would "never have the intention of injuring my opponent."
"I have great respect for my opponents and for football and that is why I never play unfairly,'' Stafylidis added. "I wish him a speedy recovery from the bottom of my heart because football needs players with his quality.''