At the wheel of his Granta Sport car, the English driver had already taken part in the WTCC Race of Hungary at Budapest, where he was stopped by mechanical failures in both races after setting encouraging lap times in the Saturday sessions.
LADA Sport plan for the current season was to make only two appearances in the world championship and focus on the technical development of the new car in view of joining for the whole season in 2013.
"Although racing is great for showcasing, it's not always the best for developing," said Thompson.
"At Budapest the Granta showed a lot of potential, but we just had a lot of new car maladies. We had the pace over one lap, which is all you can ask when you never turned a wheel!
"Our pace was somewhere around the top ten, and it was good.
"It will be interesting to see what happens at Portimão, we will treat it as two races and two test sessions, then it’s up to the team to decide whether we want to do a little more development and maybe race again or just keep on developing for the rest of the year."
The LADA Sport team will test tomorrow at Magny-Cours.