Carlos Sainz has backed his former team Toro Rosso to bounce back.

Just after the Spaniard left for Renault, Toro Rosso surprised the paddock by performing well with its new Honda engines in Barcelona testing.

However, then the sort of reliability problems and lack of performance that had become customary during the McLaren era re-emerged in Australia.

Sainz told reporters: "[Toro Rosso] were very good in Barcelona, so for me the strange one was Australia. They were worse than expected.

"In Barcelona we had them together with us and McLaren, and they have a lot of top speed here which is something that surprises me."

Sainz is 'on loan' to Renault this year, and could be pulled back to the Red Bull family for 2019 if Daniel Ricciardo leaves.

The 23-year-old has high praise for Red Bull Racing.

"It is basically still the same team as when it won four world championships in a row," said Sainz.

"The other Renault teams are trying to get closer to them, but we know that if you put a Renault engine in every car on the grid, the best would be Red Bull."

The championship continues tomorrow with the Bahrain Grand Prix.