Pascal Wehrlein has revealed the extent of his back injury in a social media post thanking Sauber for the team's hard work in helping him return to fitness.
Having missed the opening two rounds due to a lack of fitness after fracturing three vertebrae in his back in a crash at the Race of Champions in January, the German-Mauritian impressed as he finished 11th on his Formula One race debut for Sauber at the Bahrain Grand Prix.
On Monday Wehrlein posted images on Twitter showing him in a neck brace during the early stages of his rehabilitation from the injury. The 22-year-old believes taking extra time out of F1 to focus on his training played a vital role in his recovery, though he admits he was surprised by the level of his fitness in Sunday's race in Bahrain.
"I'm surprised how good it is," Wehrlein said. "But that's what we could have expected because the strength went away but it's coming back quite quickly. You can see what a big change these two weeks of training have been to me and I'm just really happy overall.
"This race was great in terms of performance and I'm really happy to come back like this, it's like I've never been away. Fitness wise, I'm feeling good. Now I feel it, of course after a long race I have some pain in my back. I'm quite tired as well, but I guess everyone is after the heat."
Wehrlein admits critics did have an impact on him but ultimately only fuelled his determination to hit back with a strong performance on track.
"Mentally, it was a great weekend," he said. "I know what I can do and I know I can be quick but the last three weeks were really difficult for me. I heard some crazy comments from other people about myself, what I should do or what they would do in my situation even though they don't know what my situation was. The best answer is to show the performance on track and to come back like this. I came back like I never had a break."
The Mercedes junior driver was replaced by Ferrari reserve driver Antonio Giovinazi in Melbourne and Shanghai but stands by his decision to sit out the first two races of the campaign.
"In Melbourne, it was not possible to drive. I wasn't there with my back, I wasn't there in terms of fitness. It was just too early, it was eight weeks after three broken vertebrae. I couldn't move for 5 weeks, so I was still recovering from my accident."