Both drivers were called up on the eve of last weekend's Bahrain Grand Prix support meeting, where Clos replaced Josef Kral at Addax and Hartley filled in for Jon Lancaster at Ocean.
Addax has remained quiet on its driver situation long-term, but AUTOSPORT understands that Clos is unlikely to continue beyond this weekend as his focus for the bulk of the season will be on his third driver duties with the HRT F1 team.
Ocean team boss Tiago Monteiro had hoped that Lancaster would be back in Portuguese team's car this weekend, as the Briton is working hard to have a budget in place to return to his race seat.
Clos, who is a former race winner in GP2, achieved a best result of 11th on his return to the category. But he hopes that the information gathered about the 2012-spec tyres will leave him in better shape for the second Bahrain event.
"After last weekend and all the efforts of the team I feel much more confident with the car," he said.
"All the feedback collected was positive, and I know better the tyres and how to deal with them.
"It is very important to have a good strategy and save the tyres for the last laps. I'm looking forward to fight for the top positions."