Publisher Gruner & Jahr, which is owned by media group Bertelsmann, controls the other 50% of the FT Deutschland.
A sale of the Pearson stake to Spiegel would indirectly increase Gruner & Jahr's stake because it also owns 25.5% of Spiegel.
Pearson's interim results at the end of July showed that FT Deutschland, which was launched in 2000, had a circulation increase of 2% to 105,000 copies.
Pearson, which owns the Financial Times, a 50% stake in the Economist magazine, and a majority stake in data provider Interactive Data Corp, is aleady in talks to sell its French business daily Les Echos to luxury goods group LVMH.