The 30-year-old has been at Schalke since 2013, and gives Watford another defensive option to consider.
Tottenham could grab a bargain as Schalke put Max Meyer up for sale.
The Algerian international is clearly more happy with his current situation at Bundesliga side Schalke.
Nabil Bentaleb will move to Schalke permanently from Tottenham Hotspur in the summer transfer window.
Manchester United, Manchester City and Arsenal stars feature prominently in our list of top players set to become free agents.
Tottenham midfielder produced his best display yet for Schalke.
The Schalke 04 attacker has been linked with a move to North London for some time now.
That is more than the previously reported buy-out clause for the Tottenham Hotspur star.
The Algerian played in a deeper role during his time at White Hart Lane.
The German youngster was linked with a big money move to Spurs in the summer.