The 23-year-old was Wanderers' stand-out player last term following his club-record move from Benfica in 2016, scoring 10 and registering eight assists in his debut campaign in the Championship.
However, the Portuguese's season came to an abrupt end in April due to an ankle injury which eventually resulted in undergoing surgery during the summer.
Costa's rehabilitation has made slow progress but Nuno says the Wolves medical team are finally seeing signs of improvement and is hopeful of welcoming him back to his squad before too long.
"Yes he's getting closer," Nuno told reporters. "We have to regard all the problems of Helder comes from last season.
"He didn't have a pre-season, he started working, then surgery, he's in the process of coming now.
"He's not totally free of pain but he's making the right steps to be inside the squad as soon as possible."