Ducati struggled for pace at the Spanish track, where world champion Casey Stoner had to settle for 11th place after a race full of problems.
Teammate Marco Melandri was 12th in what was Ducati's worst result since 2006.
The lack of long straights at Jerez did not suit the GP8 bike, and the team admitted they were expecting a tough time even before the race.
But Suppo believes the story should be different in Portugal this weekend.
"In 2007 Stoner finished third (in Portugal), 1.4 seconds behind Rossi, despite serious difficulties with the clutch," Suppo told Gazzetta dello Sport.
"We shouldn't have major problems also because there's a long straight and there are no long curves like in Jerez, the ones that give us the most difficulties because of the engine power output characteristics.
"Casey should be competitive and Marco last year classified second among the Bridgestone riders. He has to find some confidence because he has occasionally been quick, like on Saturday morning in Jerez."
Ducati were dominant in 2007, with Stoner winning 10 races on his way to the title as the GP7 proved to be a step ahead of its rivals.
Yamaha and Honda, however, seem to have closed the gap this season and Suppo admits that was only expected.
"In 2007 (technical director) Filippo Preziosi did an excellent job in interpreting the new regulations of the 800cc displacement, but it was inevitable that sooner or later the others would reduce the gap," added Suppo.
"By contrast, we are already at the maximum and we struggle to improve further. But let's not forget that we won the first race and in Losail our four bikes had the top four highest speeds."
autosport.com