The Czech Republic international joins on a season-long loan.
The club have also sent Czech Republic left-sider Daniel Pudil to Hillsborough on a season long loan.
Sky Sports are reporting that the deal is done, with confirmation due later today.
The player himself has also confirmed the deal on his official Instagram.
Pudil, who arrived at Watford from Cesena in 2012, is a left-back who can also play on the wing who has been pivotal to Watford’s rise in recent years. However, his playing time decreased last season and he is yet to feature in the Premier League this term.
Watford need to cut some of the foreign players from their squad before the Premier League squad confirmation next week and that has seen many of the names who helped them earn promotion be linked with an exit.,
For ambitious Wednesday it is another great signing. They are hopeful of a promotion tilt this term and Pudil will strengthen the left-hand side of the Wednesday team and hopefully his experience at the top end of the Championship will be a big boost to the Wednesday cause.