If the jury is still out on Michael Schumacher's Formula One comeback with Mercedes, then the next two weekends of racing in Spain and Monaco may make a verdict easier to reach.

The seven-times world champion, returning at the age of 41 and after three years in retirement, has been outqualified and beaten in the first four races of the season by young fellow German Nico Rosberg.

In Australia in March the former Ferrari ace struggled to get past Toro Rosso's 20-year-old Spaniard Jaime Alguersuari, who was racing at the Melbourne track for the first time, and ended up 10th.

After Schumacher retired in Malaysia and then just scraped a point in China with another 10th-place finish, some commentators were ready to write him off even if others refused to rush to judgement.

"People are going to say he's past it now, which he probably is," declared former great Stirling Moss, now in his 80s and convalescing after a fall down a lift shaft at home, after the last race in Shanghai.

Schumacher will be using a different chassis in Barcelona this weekend, the one he had in pre-season testing, and the car's wheelbase has been extended to allow for better weight distribution.

The German has probably put in more miles at the Spanish circuit than anywhere else over the years and won there six times, including four in a row from 2001 to 2004, during his golden years with Ferrari and Benetton.

He has also won five times at Monaco, which follows immediately after Spain. If he fails to shine there against his team-mate, with a car tailored to his requirements, the questions will become even more pointed.

"After Monaco, we'll know how his form really is," Red Bull's Australian driver Mark Webber told BBC last week. "He'll feel a bit more at home at Barcelona and Monaco.

"They're the sort of places, particularly Monaco, where you just plug Michael in and off he goes. If he's not going to be doing that this year, you can say he might be having problems coming to grips with the car."

Mercedes team boss Ross Brawn, who was Schumacher's technical director at Ferrari when the German won five titles in a row and most of his 91 race victories, remains convinced that the car and tyres are the main problems.

"He's trying to find his references and is trying to work out how to approach things," the Briton said after returning from China.

"Undoubtedly these tyres are a bit different to what he's used to and maybe, with the car and the tyres, it's not towards the way he likes to have a car, which is very responsive and very sharp.

Brawn said before the season started that he saw the same old Schumacher, determined and remarkably fit, and that is still the case even if the competition is intense.

"Our step forward in Barcelona will be bigger than you can make at each race during the flyaways (long-haul races) but it would not be realistic to expect us to suddenly be competing right at the front," cautioned Schumacher on his personal website (www.michael-schumacher.de).

"I am hoping for a better race in Barcelona than I had in China and of course I would not mind having had better results so far.

"However the good news is that after three years away, I am feeling extremely motivated. So I am clearly ready to take this challenge."

The team's own post-race analysis showed that the veteran was getting closer and closer to 24-year-old Rosberg in performance. China, the track that brought Schumacher his last win in 2006, may have been just a blip.

By lengthening the wheelbase of the Mercedes, the team should be able to hand Schumacher a car that allows him to show off his talent while also giving Rosberg more flexibility.

The concern however remains that in the past, and particularly when he was in his early years in F1 and shortly after his move to a then under-performing Ferrari, Schumacher's great attribute was his ability to drive around problems and make a poor car look good.

It could be that Rosberg has excelled in taking the Mercedes to two successive podium finishes, but it could also be that the car is not that bad either. In which case, the problem is Schumacher.

Retired triple champion Jackie Stewart, who worried before the season started about how Schumacher would handle adversity after enjoying top billing at Ferrari, said he still had faith in the German rekindling the old fires.

"The fat lady is a long way from singing,"he said at Silverstone last week.

"You are going to see (Red Bull's Sebastian) Vettel winning races, the same from Webber, the same from Schumacher when he gets his new car built around him.

"I don't think he will win world championships but I do think he will be on podiums and I think he could win a race this year," added the Scot.