The 32-year-old from Brecon will be making his first international appearance since winning gold at the Rio Paralympics in September.
He will be joined in Slovenia by Paul Davies and Tom Matthews.
"I had a long break after Rio. Training has been going well and I'm reasonably happy," said Rob Davies.
Rob Davies did win the class 1 title at the British Para Table Tennis National Championships in April, but said he is excited to get back on the international stage at the Slovenian tournament which begins on 6 May.
He continued: "The Slovenia Open is always a strong competition so I know it will be tough. My main goal for this year is the European Championships in September and that is what I am working towards."
Paul Davies, 50, from North Cornelly, won Paralympic bronze in London 2012 and reached the quarter-finals in Rio following a long absence with injury whilst Aberdare's Matthews has had his own injury woes.
He missed most of 2016 after breaking his leg, but since his return he took bronze at the Italian Open in March.
Meanwhile Swansea's Paul Karabardak, men's class 6 gold medallist in the Italian Open, is still recovering from a foot injury and will miss the Slovenia Open.
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Paralympic table tennis gold medallist Rob Davies is one of three Welsh players in a 15-strong British squad that will compete in the Slovenia Open