The 31-year-old qualified 19th after taking over the unwell Felipe Massa's Williams ahead of qualifying at the Hungaroring, and despite having trained to F1 standards and being race fit thanks to his full-time DTM drive, he is anticipating a draining race.
"Physically," he said when asked what will be the most difficult challenge to deal with in the race.
"I'm trained, but you're tense and you need to learn to relax and let the muscles relax. It's like any winter, the first day you come back – you think how did I ever drive these things and find it so easy.
"Even when I had the winter off and drove a DTM car, the first day you hurt because you're hanging on, using every muscle.
"I probably had my hardest grand prix round here in 2012, it was hot, so I'm not expecting it to be easy tomorrow.
Di Resta described the Williams team's task in qualifying as one of simplifying the learning process so he could get up to speed having never driven the 2017 Williams FW40.
He expects to take a similar approach to the race, although the absence of experience of the car on long-runs means he accepts things could go wrong.
