Lleyton Hewitt's comeback from hip surgery stumbled on Spanish clay when the former world tennis number one lost 7-6 6-4 to Eduardo Schwank in the second round of the Barcelona Open.
The 29-year-old Australia has played only one tournament since the operation at the end of January.
He was twice broken by the 59th-ranked Argentine and misses out on a possible last-four clash with French Open runner-up Robin Soderling.
The Swede is the highest-ranked player left in the tournament after a slew of withdrawals, including world number three Rafael Nadal, who has won in Barcelona for the past five years.
Nadal pulled out on Tuesday, saying he needed to rest after winning a record sixth consecutive title at the Monte Carlo Masters.