Eighth and fourth were all the four-time champion could manage after issues blighted his day.
"It was a tough day," Vettel told reporters after second practice. "This morning we had a problem with a little wing that failed and came off. We lost some track time, which was a bit costly for the afternoon, because we couldn't re-balance the car."
"I think that we've been on the back foot today," he added.
However, the former Red Bull man is confident that he will be able to fight back over the rest of the weekend.
"I'm not entirely happy with the car's balance yet, because it's a little bit too nervous all around, but I think for tomorrow we can improve," he said. "Hopefully tomorrow will be a lot stronger."
Bahrain International Circuit - Winter testing