Slow Senna’s chassis still damaged in Monaco
He was the slowest qualifier in Spain, and he remarked that "there is something wrong at the back" of his F110.
Senna retired into the gravel on the opening lap, and then confirmed to France's Auto Hebdo that the new Spanish team had not identified the car's problem in the three-day gap before Thursday's practice running in Monaco.
He was nearly two seconds slower than his teammate Karun Chandhok in the afternoon session in the Principality, where his famous uncle won no less than a record six times.
Senna, 26, won the GP2 race at Monaco in 2008.
"There is something wrong at the back and we still have not found what it is," he said.
More than 7 seconds further up the timesheets, Ferrari's Fernando Alonso was quickest once again on Thursday afternoon, ahead of Nico Rosberg and Sebastian Vettel.