In Federer's first outing for two months, the 39-year old lost to Andujar to wreck his hope of stringing a run of matches together ahead of the French Open, Wimbledon and the Tokyo Olympics
Roger Federer said it was time to go back to the drawing board after the Swiss tennis great lost the first match of his comeback-proper in Geneva Tuesday.
In his first outing for two months, the 39-year old lost 6-4, 4-6, 6-4 to Spanish clay court specialist Pablo Andujar to wreck his hope of stringing a run of matches together ahead of a series of major tournaments, namely the French Open, Wimbledon and the Tokyo Olympics.
Federer tentatively returned to the courts in Doha in March, having been out for more than a year following two knee surgeries, winning his first match before losing his second.
The 20-time Grand Slam champion was hoping to find some form on the Geneva clay but tumbled at the first hurdle in his first defeat on home soil in seven and a half years.
Federer said he would now work on analyzing his game to identify where he is falling short.
His next tournament, the French Open, starts on May 30.
However, Federer said anyone who thought he could challenge for the clay court Grand Slam title was simply "wrong".
Federer holds a record eight Wimbledon titles.
The world No 8 was cheered on by a few dozen masked spectators dotted around the Eaux-Vives center court, with the attendance limited due to local coronavirus restrictions.
The top seed took time to find his groove against the world No 75, who has four clay court titles to his name.
In the second set, Federer began to show flashes of the old magic, throwing in occasional backhand drop shots.
At 4-3 up in the final set he lost his serve and though he saved two match points, he misfired to hand his opponent victory.
Former world No 1 Federer went into the contest with a 32-match winning streak on home soil.
His last loss in Switzerland was in October 2013 in his home city of Basel against Juan Martin del Potro.
Andujar will face either Marton Fucsovics, the 2018 Geneva winner, or Swiss teenager Dominic Stricker, the 2020 French Open boys' champion, in the quarter-finals.
Stricker stunned the 2014 US Open winner and world No 46 Marin Cilic 7-6 (7/5), 6-1 in the first round Tuesday in what was the 18-year old wildcard's first senior match on the ATP tour.