Lorenzo was taken to the Medical Centre for a check up and then hospital in Buriram and later decided to pull out of the race.
It did, however, put a dent in his attempts to move into that all-important top ten - and the Spaniard is already riding through the pain barrier following his Turn 1 crash at Aragon.
Back to the front and the gaps remained minimal. Fifth on the combined time sheets was Danilo Petrucci (Alma Pramac Racing), who finished 0.050 behind Marquez to improve from P9 in FP1, with Andrea Iannone (Team Suzuki Ecstar) a further 0.018 in arrears despite a fast crash at Turn 4 in FP2.
Alvaro Bautista (Angel Nieto Team) managed to string a strong second Free Practice session together to end the day seventh fastest.
Buriram's fastest in testing, Dani Pedrosa (Repsol Honda Team), ended the opening day in eighth.
Just behind the Spaniard was FP1's second quickest man Valentino Rossi (Movistar Yamaha MotoGP), who sits in a provisional Q2 place in ninth and sported Yamaha's new fairing.
With less than a tenth splitting the top four and a second separating the top 17, there's everything to play for on Saturday.
Tune in for FP3 as the premier class fight it out for that all-important automatic entry to Q2 at 09:55 local time (GMT +7), before qualifying begins at 14:10 local time in Buriram.