New Pramac Ducati MotoGP rider Ben Spies elected to miss the final day of testing at Sepang, in order to rest his healing shoulder.
The Texan was injured at the same circuit in last October's Malaysian Grand Prix and later underwent surgery. The 2011 Factory Yamaha race winner had been absent from the track until Tuesday's opening day of 2013 testing.
Spies made his Desmosedici debut with 21 laps on day one, then rode a further 27 laps on day two, when he was 13th fastest.
"I woke up this morning and felt a little bit sore from the two days of riding and - with only starting rehab 2-3 weeks ago - it's not just my shoulder but my general physical fitness is nowhere near where it needs to be," Spies explained on Thursday.
"We need to be smart and do things the right way. We've had enough setbacks in the last few months. It's important not to go over the limits and do anything silly, or make any mistakes and dig ourselves in a hole physical instead of building forward for the next test."
The former AMA and World Superbike champion had set a best time 2.453s behind Honda's Dani Pedrosa on day two - but was only 0.892s from top Ducati rider Nicky Hayden.
"I think we did a good job over the first two days with the laps we did and quite honestly to be as close as we were to the other guys on the same bike - I was really surprised," said Spies.
"So we talked with the team this morning and thought it was the best thing [to miss the final day] to fully recover and keep going forward."
Spies added that he did not want to make set-up changes - and would not be able to draw any real conclusions about the Ducati until he can start to push harder.
"About all I can say at this stage is that the [seamless] gearbox is nice, smooth and super fast. The engine has a lot of power and the bike feels strong in straight-line braking."
The second Sepang test will be held from February 26-28.