The Brazilian defender picked up a groin problem in the 1-1 draw with Tottenham on December 27.
And the 31-year-old, who has been hampered by injuries since arriving from French club Lyon in the summer, has now had to undergo surgery.
"Marcal is inside the gym. He had an operation, (so he needs) some time more," said Nuno.
"We have time, to first heal. He has to be free of pain. Then, we'll start re-integrating him and getting fitness levels again. I think more weeks, some more weeks in front of him yet.
"It was against Tottenham. He slipped on his left leg and felt a strong pain in the abdominal area.
"So, it required treatment and an operation to solve the problem."
Daniel Podence is still nursing a calf injury while Raul Jimenez has 'started jogging'. Jonny Castro Otto took part in a warm-up at Compton this week.
Nuno added: "Daniel is starting the outside work with (assistant fist-team coach) Joao Lapa.
"He's getting back his fitness, how he reacts to training sessions. Progressively, he'll be joining us.
"Raul has started jogging and he's improving. He's started some physical work in the gym – the treadmill.
"We cannot put a time yet, but hopefully things keep improving."