Watford manager Quique Flores has revealed that the club allowed Matej Vydra to leave on loan as he failed to adapt to his style of play.
The Czech Republic international scored 16 times in 31 Championship appearances in Watford's promotion campaign last season, but joined Reading on loan on transfer deadline day after falling out of favour with the Hornets boss.
The Spaniard told reporters that he would not stop players that want to play regular first-team football that he could not guarantee from leaving the club.
Flores said: "I think he did not adapt to the team. I need to keep players here who believe in the work 100% and I felt Vydra was working but was not convinced about the ideas we have. In this case I had to bid for players who would train 100%."
Watford look to win their first game back in the Premier League on Saturday as they host Swansea City.