Lewis Hamilton says he has not seen a big change in Valtteri Bottas in 2019.

"For me it's the same Valtteri as before, except that now he has a beard," the Mercedes driver smiled.

However, after a full winter of being criticised for his poor performances in 2018, amid speculation he will be replaced by Esteban Ocon for 2020, Finn Bottas won in Melbourne and issued a "f**k you" to his critics on the radio.

He said in Bahrain: "I can say for sure that something in my mindset has changed for this year."

Hamilton, Bottas' Mercedes teammate, is not so sure.

"Whether it's really a new Valtteri or not, we will see," he said. "But I never saw him as weak anyway.

"Melbourne doesn't change anything for me. Valtteri was already strong in 2018, he was just unlucky in a few races.

"I never doubted for a moment that he would win again," Hamilton added.

Former F1 driver Nick Heidfeld, though, says Bottas was extremely strong in Melbourne.

"He not only won but also in qualifying he looked like the stronger driver, even though he was not on pole," the German told Sky Deutschland.

"He probably did a lot over the winter in all areas to take advantage of the opportunity he has at Mercedes," Heidfeld added.

Hamilton also hit out at Sebastian Vettel in Bahrain, after the Ferrari driver declared in Melbourne that the reigning world champion had appeared "bored" during the 2019 season opener.

"Sometimes it's easier to blame other people when things are not going so well for you," Hamilton said of the German.