Bale has been on the sidelines since November with an ankle problem, but was pictured going through a series of training drills on Real Madrid's official Twitter page at the weekend.
It has been suggested that the Welshman could be on the bench for Real Madrid's Champions League last-16 first leg against Napoli on Wednesday night, but Zidane has insisted that he will take no chances with the attacker's fitness.
"It's the first week that he's trained with the group. He's good, he's good physically and mentally, which is the most important thing," Zidane told reporters.
"We'll see if he can be in the squad or if he'll be there at the weekend," he added, referring to the impending visit of Espanyol in La Liga. "At the same time, after two or three months out, we have to be very careful with Gareth."
Bale, 27, scored seven times in 16 appearances for Real Madrid before suffering damage to his ankle in November's Champions League group match with Sporting Lisbon.