Massa described Button's Tuesday performance as 'incredible', but the Brazilian was the first and only man to lap in the 1m17s this week on the third day of testing.
Although Massa lapped over a second quicker than Button had, the Ferrari driver believes that given the track conditions on Tuesday and the fact that Button set his time using the hard tyres, the McLaren's pace was still a benchmark.
"I still believe his lap was incredible," said Massa of Button's effort after the third day of testing.
"On the hard tyres on the first day on the dirty track and everything, it really was a quick lap. I didn't have the car to do this lap time on the first day.
"I didn't even try to work for the lap time, but I think it was impressive.
"I think many people are thinking the same about me now, but I think we just improved the car on these days. I think it was a good lap I did, but we can't say what we're going to have at the beginning of the championship.
"I have my feet 100 per cent on the ground."
Although Massa admitted that the first days of work with the F138 had been positive, he refused to believe that Thursday's fastest time meant much.
"It's going in the direction I was hoping but the races are where it counts," he said. "In the tests I don't think it counts so much.
"It's always nice but it doesn't count so much. I think our feet are on the ground and we need to work 100 per cent to improve the car for the first race."
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