Watford have signed right-back Jeremy Ngakia after his contract expired with Premier League side West Ham United earlier this summer.
The 19-year-old made five starts last term and most recently played in their defeat by Wolves on 20 June.
Meanwhile, striker Cucho Hernandez has joined Spanish side Getafe on loan.
The 21-year-old has previously spent time on loan at SD Huesca and Real Mallorca, with the deal including an optional break clause in January.
Colombia international Hernandez scored five goals in 24 games for Mallorca in La Liga and cup last term.
Elsewhere, Watford have confirmed Dimitri Foulquier's move to Granada, after an initial loan move in January.
The La Liga club had already announced the signing last month, on a three-year deal, for an undisclosed fee.
Find all the latest football transfers on our dedicated page.