Ben Spies admits a fall on the second day of MotoGP testing at Sepang left him having to contend with shoulder spasms across the final two days.
Spies was forced to miss his final two races of 2012 after a heavy crash in last year's race at Sepang left him with an AC shoulder separation, a cracked rib and bruising to the lung.
He underwent successful surgery and returned to MotoGP action in this week's test, only for a relatively minor Turn 1 fall to aggravate his injury.
"I made a small mistake yesterday which dug my elbow into the ground," he said.
"It was an easy crash but it upset my back and shoulder a little bit, so I had a few spasms yesterday and couldn't do a whole lot of riding."
After ending the final day 14th, and more than half a second off team-mate and MotoGP rookie Andrea Iannone, Spies admitted that his lack of fitness was hampering his speed.
"Anybody in our shoes would obviously like to be a little higher up the timesheets," he said.
"Today we rebounded a little bit and got to put some laps in, but had a couple of little problems with the bike and lost the last hour.
"All in all, it wasn't too bad and our quickest lap was actually set on old tyres - so that was good - but we'd like to be faster.
"For me right now, I just want to get back to 100 per cent fitness and get used to the bike."