Celtic are interested in Fenerbahce midfielder Stephen Appiah.
BBC Sport says the Scottish champions face competition from a number of other clubs for the 26-year-old Ghana international's signature.
Schalke, who finished runners-up in Germany's Bundesliga, have been linked with Appiah, who helped Fenerbahce to the Turkish title this season.
Appiah played for his country in last year's World Cup finals.
However, he is likely to be just one of a number of players on Celtic manager Gordon Strachan's list of possible summer signings.