First, try to understand why he is shy and how exactly is his shyness preventing him from contributing to progress. Is he shy by design, even outside work? Or does he feel like he does not have the psychological safety to speak up? You can get a sense for this by spending some time with him 1:1 outside work and getting to know him as a person.

Second, examine your own relationship with him. Does he trust you as a manager? Is he open to your feedback? If not, you should work on building that relationship - you know how you can/should do that.

Finally, once you have that relationship and understand the root cause, give him constructive and candid feedback. If he's shy by design, you could have a constructive conversation about it - does he perceive it as a weakness? Does he realize that it might be holding him back? Make him think and align on a plan to help him overcome it. If he's not seeing psychological safety in the team, dig into how the team works and make a plan for yourself to fix that.

Then make this part of your regular 1:1s and track progress. Important that he sees that you are vested in his success and are genuinely helping him.

Needless to say, this assumes that you want him on the team and help him become a better version of himself.