Valentino Rossi has confirmed Yamaha will use their 2016 bike as the base for next year's model after they struggled to keep pace with Repsol Honda this season.
Rossi was a championship contender last year but fell away in 2017 as the Italian encountered problems across the 18 races.
The initial signs looked good as team-mate Maverick Vinales won three of the opening five grands prix, with Rossi claiming three podiums.
However, as the season wore on their competitiveness waned, with Rossi particularly struggling - the seven-time world champion only finishing on the podium on three further occasions.
Rossi finished the campaign fifth in the riders' standings with 208 points, 90 behind eventual champion Marquez.
In order to bridge that gap the team have discarded the 2017 chassis and intend to use the previous year's model as they prepare for the new season.
"We tried the old bike, the one from 2016," Rossi told Italy's Radio Deejay. "We deliberated and we were all agreed the 2017 bike was worse.
"We still have to see what the new bike will be like, there will be something interesting. But the base will be the bike from 2016.
"Now is a critical moment. Between now and February, Yamaha needs to make a big leap forward."