Trending @Infosys; Job offer from Client

My contract with the client is ending this month. There was a job opening aligning with my profile in their portal and I had applied for it. I have cleared the interview but the client is asking for an NOC from Infosys before they can give me the offer letter. I am worried about bringing this up with my manager without a written offer. What should I do? Has anyone else gone through a similar situation?