The winger has been linked with Leeds and his manager can see him leaving.
And the same source suggest Leeds United could close a deal for the 24-year-old by the weekend.
Indeed, it is reported Leeds have had a £1.25 million bid for Dallas accepted - and the Brentford boss's comments suggest a deal could certainly be likely.
Dijkhuizen is quoted as telling BBC London: "He is not here because of private reasons and not linked with a departure.
"He has a year left on his contract and he doesn't want to sign so he might leave in the next couple of weeks."
Leeds are a couple of pieces short of a full set at Elland Road, with a wide man generally considered to be the position the club needs to strengthen in the most.
The Leeds hierarchy have added to the Yorkshire side's midfield, defence, goalkeeping department and final third so far this summer but a winger is still required for Uwe Rosler. Dallas could be the man to fill that void and, judging by Leeds' astute team performance against Everton, the rest could proceed like clockwork.
Should United seal a deal for the Brentford man, it would close pre-season in the perfect fashion following their 2-0 win over the Toffees - something that has boosted morale among fans considerably.