Ravi Zacharias' wife has said her husband is having a challenging and painful recovery from surgery. 

The Christian apologist has an operation last month to correct issues with his spine. 

In an update on social media, his wife Margie thanked those who have been praying for his recovery but said it's been hard. 

"Ravi is progressing in his healing, but at a much slower pace than he had expected based on his past experience," she tweeted on behalf of her husband. 

"Perhaps since Ravi is 18 years older now than when he had his previous back surgery, the healing takes more time. His pain continues to be severe, especially during the night, which makes the nights very long and difficult.

"We are thankful that Ravi has the expertise of two pain management doctors, including his brother Ramesh. 

"Please keep praying for Ravi, especially his nights. This is a challenging time, and there is still a long way to go before he will be able to pick up his itinerary."

She also said prayers and encouragement from supporters "means the world" to them.