The 26-year-old, who joined Marussia as their official reserve driver ahead of the Canadian Grand Prix, will replace Roberto Merhi in the opening practice session, before handing his cockpit back to the Spaniard for the rest of the weekend.
"Running Fabio in a Free Practice 1 session is a planned opportunity that we have all been working towards for some time," Marussia team principal John Booth explained. "We have enjoyed welcoming him into the team over the past few races and it will be interesting to gain his feedback on the car and assess his performance."
Leimer, who clinched the GP2 Series crown in 2013, added: "On this most difficult of weekends for the team, I am very appreciative of their decision to continue with my planned FP1 session.
"I'm looking forward to the opportunity and I hope I can make a positive contribution to the engineering programme for the weekend."
Marussia described the decision as a 'scheduled step' in Leimer's induction to the team, saying it would help him be ready to deputise should he be needed on a race weekend.
Alongside Leimer, last year's GP2 champion Jolyon Palmer is once again set to take part in FP1 for Lotus.