Mercedes' vice-president of motorsport Norbert Haug has admitted that the marque's F1 performances, while improving, are still falling short of where they ought to be.

Nico Rosberg claimed back-to-back fifth places in the Chinese and Turkish grands prix, and led the race for 15 laps in Shanghai, but Haug insists that Mercedes is still failing to live up to expectation when it comes to taking on the likes of Red Bull, McLaren and Ferrari. Rosberg currently sits ninth in the championship standings, with 20 points, while Mercedes is fifth in the teams' competition, with 26 points from four races.

"We were better than during the first two GPs, but still not good enough for where we want to be," Haug confessed to India's ibnlive.com, "We have to, and we will, improve further, but this takes time for a team that was completely re-structured one-and-a-half years ago."

Along with almost every other team on the grid, the Brackley-based outfit is bringing development parts to each race, and Haug is confident that, under Ross Brawn's direction, the squad can begin challenging at the very front.

"We are working on further improvements, and I think we are heading in the right direction," he claimed, "The third and fourth races saw the team start twice from the second row on the grid, and score two fifth-place finishes, [so] we will build on that. We have quite a few things in the pipeline, but Ross will hit me if I tell, so [there's] no chance that I can be specific."

While Rosberg has begun to regularly threaten the top five, veteran team-mate Michael Schumacher is again struggling to match up to his young compatriot. The seven-time world champion has just six points to his name, sits eleventh overall and has missed the final phase of qualifying in three out of four races this season. With rumours again circulating that Schumacher's time in F1 is nearing an end, however, Haug insisted that the 42-year old could still be a force to reckon with.

"Absolutely, he will succeed again," he claimed, "He has the speed, the talent and the willpower to do so."