Michael Schumaker is making serious attempts to return back to Formula One race. He has sustained serious neck injuries in a motor cycle accident in February. A day after announcing he was ending retirement to temporarily replace injured Ferrari driver Felipe Massa, Schumacher's return was contingent on passing a fitness and other medical tests that could take several days, his doctor Johannes Peil said on Thursday.``Had Michael not worked so hard in recent months, all this would not have been possible,'' Peil said.