Nicky Hayden appeared to lose ground during Monday's Catalunya MotoGP test, when he lapped slower than he had during the race and was left 14th out of the 15 riders.
The 2006 world champion claimed his best result of the season so far with tenth place in Sunday's grand prix, but had hoped for much more after starting the weekend in a strong sixth position following major set-up changes to his Desmosedici.
Hayden slipped back to tenth place in Saturday's second free practice, then 13th in qualifying and 14th in Sunday morning warm-up - before breaking back into the top ten in the race - but the decline continued on Monday.
Worryingly, Hayden was the only rider present not to lap faster than he had in the race - despite a mammoth 98 laps of the Barcelona circuit - and wasn't sure why.
Nicky must now hope that off-track analysis of the data gathered can provide clues to the path ahead.
“It wasn't the day I had hoped for, seeing the progress we had made over the weekend,” admitted Hayden. “In Saturday morning's practice, when it was a little cooler and the conditions were similar to those of today, I lapped in 1min 43.6sec while here today I haven't gone under 1min 44sec and right from the start I didn't have the same feeling as I had over the weekend. I don't know why, also because we worked so hard, but I hope that the data collected is of use to the engineers so we can prepare well for Assen.”
Hayden's best lap time, a 1min 44.157sec, was 1.9sec slower than Repsol Honda's Andrea Dovizioso. New MotoGP rider Gabor Talmacsi was the only rider slower than Hayden.
Hayden's team-mate Casey Stoner was fifth fastest.