Former St Mirren left-back Carey, former Portsmouth winger Ciftci and Dutch centre-back Vorstermans all started Friday's pre-season friendly defeat to Energie Cottbus in Germany.
The Bundesliga 2 side, who are further on in their pre-season preparations, scored in each half and also hit the bar twice as United were given a testing run-out.
United boss Jackie McNamara confirmed Carey will now make the journey to Spain as United continue their pre-season campaign, while he is yet to make decisions on Ciftci and Vorstermans.
"Graham Carey will definitely come to Spain with us," said McNamara.
"Nadir we have to speak about, whether or not he can come with us or whether he has to go back to Holland.
"Ismo was in for game time and for us to have a look at him.
"We'll sit down later and see what we're going to do."
Meanwhile, Hibernian warmed up for their Europa League opener against Malmo in Sweden next week with a goalless draw against Raith Rovers in Kirkcaldy.