Vossen has returned to pre-season training with Genk after missing out on their first few friendlies as his future with the club remained in doubt.
Genk turned down a €4million bid from Boro for their 25-year-old frontman, insisting they want more than double.
That prompted an angry reaction from Vossen, who wants to move to Boro, and he has reiterated that desire to leave after playing the last half-hour of their friendly win over Al Shabab.
"The coach asked me what I would be doing after there was no green light over my future and I said I would play," Vossen told Het Laatste Nieuws
"The Middlesbrough avenue is certainly not closed, there are still options.
"I am not feeling good here and I am confident I can leave."
Middlesbrough have just spent nearly £3million on Spanish striker Kike, but it is understood they remain interested in Vossen, who is a long-term target for the club.