Mercedes struggled to find a suitable auto balance in the opening week and while the team's fortunes appeared to improve with a raft of aerodynamic updates introduced for week two, Hamilton suggested that the gap to Ferrari was "potentially half a second" after the final day of pre-season testing.
Kubica was preparing for the 2011 season when he suffered a horror injury in a rallying crash during pre-season, and it has taken eight long years to return to the top level of single seater motorsport, and he feels this weekend's Australian Grand Prix will be like a second debut after such a long time away.
Mercedes fought back and things were in the balance. "We think they're going to be strong because Honda looks strong now as well and they've always had a good auto". The British driver is once again the man to beat after he picked up an incredible fifth world championship last season.
Sebastian Vettel now has the support he needs to win the title for Ferrari.
Across the eight days of the pre-season testing in Barcelona last month, the Italian team set the fastest times and emerged with a vehicle that was roughly 0.3sec quicker than the favourites.
"But having said that obviously we can't do better than last year's result". 'This is going to be the toughest battle yet, ' he claimed.
"In the end we are racing for Ferrari and that means we will try to get Ferrari back to where we've been trying to get it back to the last couple of years. We have experience, it's no coincidence that we are world champions so we have to be diligent and stay balanced", added Hamilton, who has won twice in Melbourne, in 2008 and 2015.
The four-times champion will bid for a third successive win at Albert Park's season-opener, having foiled pole-sitter Hamilton amid a virtual safety auto deployment past year.
One aspect he clearly takes strength from is the continuity in terms of retaining Valtteri Bottas as his teammate for a third season.
All 20 drivers and their team bosses were met by thousands of supporters at the inaugural season launch event in Federation Square on Wednesday.
Meanwhile, Vettel sees Charles Leclerc, who joined Ferrari from Sauber in a swap for the experienced Kimi Raikkonen.More news: Facebook, Instagram and WhatsApp still down for many users across the world