Williams: Di Resta the best option for "tough" late call-up

Di Resta will take over the car, which will run as number 40, from the start of qualifying after Massa felt unwell.

Di Resta has not driven the FW40 on track, although he does have some knowledge of hybrid technology after driving the 2014 FW36 test car used by Lance Stroll.

Williams believes that the Scot has the experience with which to deal with his last-minute substitution role.

"I'm sure he's probably fairly nervous," said Williams. "But Paul is an experienced driver, and I couldn't feel happier actually that we have someone of Paul's calibre and experience.

"Even though he may not have taken part in a race weekend for a couple of years, he's driven this era's hybrid cars, he's driven in our 36, so I have confidence.

"Of course it's going to be tough. He hasn't had any practice, and he's got to get straight into qualifying in an hour's time.

"I'm sure there are some nerves there, he hasn't had much time to get ready, but I have utter confidence in him that if anyone ca do this, Paul can."

Williams said that modifying the car for di Resta was not a big issue despite the lack of time before qualifying.

"It's not as complicated as you probably imagine," she said. "There are a few changes to make inside the cockpit.

"Obviously Paul's a little bit taller than Felipe, but they rehearsed it last night, and it takes about 40 minutes to make the changes.

"Paul has his licence, that's all sorted, and obviously in preparation last night we knew that potentially this could be an option for us. So we made sure everything was in place."