Stuttgart - Michael Schumacher is continuing preparations for his comeback to Formula One at home in Switzerland, the seven- time world champion's spokesperson confirmed Friday.

The 40-year-old, who is in a race to be fit in time for the European Grand Prix in Valencia on August 23, completed two days of karting before returning home.

"Michael is working in his fitness studio with his physiotherapists," Sabine Kehm told German Press Agency dpa.

Schumacher is set to replace the injured Felipe Massa in the Ferrari cockpit in Spain after the Brazilian was injured during qualifying for last month's Hungarian Grand Prix.

However, Schumacher has not raced in F1 since 2006 and needs to get the all-clear from doctors before he will be allowed return to the sport. (dpa)