Aitken is currently the team's reserve driver and will now make his F1 debut at the penultimate round of the 2020 season. He is no stranger to the FW43, having taken part in an FP1 session earlier in the season at the Styrian Grand Prix. Alongside his reserve driver duties, Aitken has been competing in F2 this year, scoring two podiums and eight other points finishes.
"Firstly, I want to say a huge thank you to everybody at Williams for giving me this opportunity," said Russell. "I might be wearing a different race suit this weekend, but I'm a Williams driver and I'll be cheering my team on every step of the way.
"I see this as a great chance to learn from the best outfit on the grid right now and to come back as an improved driver, with even more energy and experience to help push Williams further up the grid.
"A big thank you also to Mercedes for putting their faith in me. Obviously, nobody can replace Lewis, but I'll give my all for the team in his absence from the moment I step in the car. Most importantly, I wish him a speedy recovery. I'm really looking forward to the opportunity and can't wait to get out on track this week."
"I'm absolutely over the moon to have the opportunity to make my debut with Williams this coming weekend," said Aitken, "and I am extremely happy for George to have his chance too!
"I really mean it when I say I've felt very much at home here since I joined Williams earlier this year, so to get my chance to help the team try to achieve that elusive points finish is an extremely satisfying occasion to say the least.
"I'll be doing all I can to prepare in the coming days, but truthfully, I feel like I have been ready since Melbourne. I also want to wish Lewis well in his recovery, and good luck to George getting the chance to drive the Mercedes this weekend."
"Our long-term partnership and George's affiliation with Mercedes is no secret," said Acting Team Principal, Simon Roberts, "and so I'm delighted George has this unique opportunity to join Mercedes, the current Constructors' Champions.
"We have been working hard to ensure that an agreement could be made with Mercedes to allow him this fantastic opportunity. George very much remains a Williams driver and we look forward to him returning to us fresh from this experience and wish him a successful race this weekend.
"We are also thrilled this means we are able to give another British talent in Jack Aitken the opportunity to make his Formula One race debut. Jack joined Williams at the start of this season, and despite COVID-19 restrictions meaning we haven't been able to interact with him as much as we would like, he has quickly become a much-liked member of the team. We look forward to seeing him build on his previous experience driving the car in practice, to see what he can do in a qualifying and race situation."