The 28-year-old has made 13 Bundesliga starts this season as Schalke look set to secure an automatic qualifying spot for the UEFA Champions League.
However, Heldt confirmed on Friday that the defender's contract will not be renewed at the end of the campaign.
"During our meeting I told Tim that we will not renew his expiring contract," he told the club's official website.
"He has taken this decision very well, although I realise that as a message for a player this is never nice.
"But I know that Tim will try in the remaining two games to give 100 per cent in order to help the team.
"I thank Tim already once before for his time at Schalke, he has always given everything and is an outstanding character for the club."
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