Deputy team principal Bob Fernley has admitted a decision on a second driver will be announced early next week and be the result of a shoot-out between former driver Adrian Sutil and current reserve Jules Bianchi.
Sutil, with the Silverstone-based marque for five years before being axed at the end of 2011, was in the car yesterday, with Bianchi taking up the wheel today.
Fernley said: "We'll try and get all the information to the shareholders this weekend and then it's their decision."
Di Resta's only concern is that his team-mate drives the team on. "I know both very well. They're both good people, and they've both been part of the team for a long time," said Di Resta.
"It's all up to the board members. They make the decision as to who they want to partner me.
"I'm very supportive of whoever it might be as long as they're pushing me on and they're a team player; that's the important part," Di Resta added.