Nigerian forward Taiwo Awoniyi was taken to hospital after suffering a serious head injury during Mainz's 1-0 loss against Augsburg in the Bundesliga on Sunday.
Liverpool loanee Awoniyi, 22, was left briefly motionless after landing awkwardly following a clash of heads with Augsburg defender Felix Uduokhai in the first half.
Awoniyi was stretchered off with his neck in a brace after a long delay while he received medical attention on the pitch.
Mainz said Awoniyi, a former Under-17 World Cup winner, was responsive and taken to hospital for tests. Awoniyi has yet to make an appearance for Liverpool since joining the club in 2015, spending numerous spells on loan in Germany, the Netherlands and Belgium.
Augsburg moved seven points clear of the relegation play-off place with just three games to play after striker Florian Niederlechner scored the only goal just 43 seconds into Sunday's match.
Mainz stayed three points above the bottom three. They came closest to equalising when French striker Jean-Philippe Mateta rounded the Augsburg goalkeeper but had his shot cleared off the line by defender Philipp Max.
Mainz face second-placed Borussia Dortmund on Wednesday before Saturday's crucial home match against Werder Bremen, who are second from bottom and three points behind them in the table.
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