The 30-year-old has been at Schalke since 2013, and gives Watford another defensive option to consider.
The Baggies have been linked with a move for the Leeds left-back Charlie Taylor.
The former German international would be a canny addition for Leeds United if they earn promotion.
Sunderland are believed to be interested in the versatile German.
Left-back Dennis Aogo, who was being touted as a potential Anfield addition in January, will move permanently to Gelsenkirchen.
Will Schalke sign Liverpool target Dennis Aogo despite his knee injury? – Quite likely after what general manager Heldt said.
Liverpool target Dennis Aogo has suffered a cruel blow.
A former German international was killed as a terrorist in Syria last month, it has been revealed.
Liverpool have been linked with signing Dennis Aogo.
Dennis Aogo of Hamburg is a much better long term replacement for Patrice Evra at Manchester United than Leighton Baines.
Loic Remy was a target of Liverpool back in 2014, but failed a medical with the Reds.
The Leeds United striker impressed in Tuesday's narrow win over West Brom.
West Bromwich Albion lost 1-0 at Leeds United last night.
Premier League leaders Liverpool will host Red Bull Salzburg in the Champions League tonight and Jurgen Klopp will be watching Szoboszlai closely.
Leeds United winger Jack Harrison played alongside Spain legend David Villa during his time in the MLS at New York City.
Tottenham Hotspur reportedly wanted to raid Dinamo Zagreb 11 years after bringing Luka Modric to the Premier League but Olmo didn't follow in his footsteps.
Liverpool boss Jurgen Klopp could recall Alisson back to his side's starting line-up.
The Liverpool defender is likely to play no part in tomorrow's Champions League encounter.
Dele Alli is not guaranteed to start tonight as Tottenham Hotspur host Bundesliga leaders Bayern Munich in the Champions League.
Arsenal drew 1-1 away at Manchester United on Monday night.