Former world No.3 Stan Wawrinka's French Open preparation suffered a setback after the Swiss was beaten 6-4 6-4 by American Steve Johnson in the opening round of the Italian Open.
Wawrinka, who was making his first appearance since February after recovering from a persistent knee injury, committed 30 unforced errors as he struggled to rediscover his rhythm on his return to clay.
World No.55 Johnson, brimming with confidence on the back of his title defence in Houston, converted his two break point opportunities to wrap up the match in an hour and 21 minutes.
Wawrinka curtailed his season in August last year after battling injury through the grasscourt campaign, which ended with opening round exits at Queen's Club and Wimbledon.
The three-times grand slam winner returned to action at the Australian Open in January but hobbled to a second round exit.
Wawrinka reached the semi-finals of the Sofia Open in February but followed that with early exits at Rotterdam and Marseille, the second through an injury retirement.
The 33-year-old said he will need to be more patient on his latest return from the sidelines, having only started practicing 12 days ago.
"I had a lot of hesitation with my game and it obviously makes a big difference in the way I move and the way I play," Wawrinka, who finished runner-up at French Open last year, said.
"I think when I came back in Australia it was quite clear I wasn't ready at all. But for me it's important to play matches to test myself playing against the top guys.
"It's positive to see that the knee was doing okay, but now I need a lot of time to work on my fitness. Today was tough but I'm really happy to see where I am right now."
