The Team Sky rider went down around 35km from the finish after a touch of wheels on the category two ascent of Cote de Saint-Uze.
The Welshman was quickly back riding and finished 11th to remain 19 seconds behind overall leader Michael Matthews.
"He was able to stand up straight away and get back on the bike," said Team Sky sport director Nicolas Portal.
Cofidis rider Nacer Bouhanni, who was demoted from first to third on stage two after changing his line in the bunch sprint, rode cleanly to victory in Romans-sur-Isere.
Trek rider Edward Theuns was second and Lotto Soudal's Andre Greipel third, with Britain's Ben Swift sixth for Team Sky.
The riders tackle Mont Ventoux in Provence in Friday's 195km stage.
The legendary mountain pass comes early in the stage to Salon-de-Provence.
Stage four result:
1.  Nacer Bouhanni (Fra/Cofidis)           4hrs 42mins 29secs
2.  Edward Theuns (Bel/Trek)              Same time
3.  Andre Greipel (Ger/Lotto)
4.  Alexander Kristoff (Nor/Katusha)
5.  Michael Matthews (Aus/Orica)
6.  Ben Swift (GB/Team Sky)
7.  Nikolas Maes (Bel/Etixx - Quick-Step)
8.  Tony Gallopin (Fra/Lotto)
9.  Youcef Reguigui (Alg/Dimension Data)
10. Roy Curvers (Ned/Giant)
Selected:
11. Geraint Thomas (GB/Team Sky)   Same time
Overall classification after stage four:
1.  Michael Matthews (Aus/Orica)             14hrs 24mins 15secs
2.  Tom Dumoulin (Ned/Giant)               +14secs
3.  Patrick Bevin (NZ/Cannondale)         +19secs
4.  Jon Izagirre (Spa/Movistar)
5.  Geraint Thomas (GB/Team Sky)
Selected:
9.  Richie Porte (Aus/BMC Racing) +27secs
17. Alberto Contador (Spain / Tinkoff)      +33secs
18. Simon Yates (Britain / Orica)                    +37secs
Britain's Geraint Thomas remains fifth in the Paris-Nice race despite crashing on stage four.