Fulham defender Hughes suffered a shoulder injury in Friday night's 2-1 defeat to Serbia in Belgrade. Manchester United defender Evans has a groin problem and Rangers striker is struggling with a knee injury.
Hughes will have a scan on his shoulder while Evans said he is hopeful of being fit to face Slovenia at Windsor Park. Hughes flew straight to London for the scan while the rest of the squad travelled to Belfast.
"It is now up to the medics - it's fingers crossed that the scan gives me the all clear and I'll rejoin the rest of the boys in Belfast," said Hughes. Evans came off late in the game after feeling a "tightness" in his groin while Lafferty admitted he took a gamble starting in Belgrade.
"I had been training with it and I don't think I should have been playing, but I gave it a go and it backfired," said Lafferty. With fellow striker David Healy suspended for the Slovenia match, Lafferty's fitness becomes key for Northern Ireland boss Nigel Worthington.
Rangers midfielder Steven Davis missed the Serbia game with a hamstring injury but he could return to bolster Worthington's squad.