Valentino Rossi's landmark 350th MotoGP event got off to a poor start in Friday's free practice sessions, with Maverick Vinales and Marc Marquez leading the way ahead of the Argentina Grand Prix.
Movistar Yamaha rider and seven-time champion Rossi had been plagued by front-end issues throughout pre-season training, but still managed an impressive third-placed finish in the opening Grand Prix of Qatar.
But on the 15th anniversary of his victory in the maiden MotoGP event, Rossi endured two difficult sessions at the Autodromo Termas de Rio Hondo.
The Italian posted times a fastest time of one minute, 41.311 seconds to finish in 16th place, though team-mate Vinales made up for Rossi's shortcomings.
Fresh from his victory in Qatar, the 22-year-old topped the timesheets at 1:39.477secs, with reigning champion and Repsol Honda rider Marquez 0.301secs back.
Rossi's disappointing finish was not the only surprise of the day, with fellow big names Dani Pedrosa (13th), Andrea Dovizioso (14th) and Jorge Lorenzo (18th) also struggling ahead of Saturday's qualifying sessions.
Alex Rins - remarkabley racing with a fractured ankle - was 20th.