Bernie Ecclestone has warned Formula One fans not to expect too much from the returning Michael Schumacher.

The seven-times world champion is due to deputise for Felipe Massa at Ferrari while the 28-year-old Brazilian continues his recovery after fracturing his skull.

After almost three years in retirement, Schumacher will make his eagerly-anticipated return in the European Grand Prix at Valencia on August 23 after answering Ferrari's call to arms.

However, Ecclestone feels the 40-year-old German legend may find it difficult in a car that has not been a frontrunner this season, despite Kimi Raikkonen's second place in Hungary nine days ago.

He told Sky News: "I don't think he (Schumacher) would have thought about taking it on if he didn't think he could be competitive.

"The car's not competitive for a start, so he's got a bit of an uphill struggle.

"But he'll be there for as long as Felipe can't drive. As soon as he's back in business then Michael will give the seat over to him."

Massa, who returned home to Sao Paulo yesterday nine days after his accident in qualifying for the Hungarian Grand Prix, is expected to be out of action for at least four races.