Roanne - British rider Adam Yates moved in to the overall lead at the Criterium du Dauphine following Wednesday's tricky 26.1km time-trial after his compatriot Chris Froome was seriously injured in a high speed crash during a practice run before the start of the fourth stage.
The four-time Tour de France winner was blown into a wall by a gust of wind and reportedly suffered at open fracture of the femur.
Team Ineos said Froome would miss the Tour de France due to his injuries with the 34-year-old helicoptered to hospital after lengthy treatment at the scene.
"He is in a very, very serious condition," said a sombre Ineos pricipal Dave Brailsford.
The stage itself was won by Belgian Jumbo rider Wout Van Aert in 33min 38sec, ahead of American rider Tejay Van Garderen at 31e with Dutch all rounder Tom Dumoulin in third at 47s.
"It's a first WorldTour race win. I can't believe it," said Van Aert, who is ninth in the overall standings at 30sec.
"I didn't know it was possible to win on this level so I'm super happy," said the 24-year-old former cyclo-cross champion who has come second on two previous stages here.
Yates, 26, actually finished sixth on the day to claim the yellow jersey in a race where he came second last year.
"That was a good time and a good day for me," said Yates, who will race the Tour de France.
"We have one sprint stage tomorrow, so hopefully the sprint teams will help us control, and then it's straight to the mountains," he said of the eight day route that finishes with two major days of climbing this weekend.
"We're in the jersey now and hopefully we can hold it all the way to the end."
Yates leads overnight leader Dylan Teuns by just four seconds, Van Garderen is third at 6sec while Denmark's Jakob Fuglsang of Astana is just 7sec back.
France's Thibaut Pinot in sixth at 25s and Nairo Quintana of Colombia in 10th at 40s, stand out as potential eventual winners too.
Thursday's fifth stage is a 201km ride through flat planes.
Results and standings after stage 4 of the Criterium du Dauphine on Wednesday, a 26.1km time trial around Roanne:
1. Wout Van Aert (BEL/JUM) 33min 38sec, 2. Tejay Van Garderen (USA/EF1) at 31sec, 3. Tom Dumoulin (NED/SUN) 47, 4. Steven Kruijswijk (NED/JUM) 49, 5. Emanuel Buchmann (GER/BOR) 51, 6. Adam Yates (GBR/MIT) 56, 7. Julian Alaphilippe (FRA/DEC) 59, 8. Nils Politt (GER/KAT) 1:05, 9. Jakob Fuglsang (DEN/AST) 1:07, 10. Remi Cavagna (FRA/DEC) 1:10
Selected: 11. Richie Porte (AUS/TRE) 1:19, 12. Thibaut Pinot (FRA/FDJ) 1:21, 14. Dylan Teuns (BEL/BAH) 1:23, 18. Nairo Quintana (COL/MOV) 1:36
1. Adam Yates (GBR/Mitchelton) 12hr 27min 26sec, 2. Dylan Teuns (BEL/BAH) at 4sec, 3. Tejay Van Garderen (USA/EF1) 6, 4. Jakob Fuglsang (DEN/AST) 7, 5. Steven Kruijswijk (NED/JUM) 24, 6. Thibaut Pinot (FRA/FDJ) 25, 7. Emanuel Buchmann (GER/BOR) 26, 8. Alexey Lutsenko (KAZ/AST) 30, 9. Wout van Aert (BEL/JUM) 30, 10. Nairo Quintana (COL/MOV) 40
Selected: 11. Wout Poels (NED/INE) 40, 12. Richie Porte (AUS/TRE) 54, 13. Dan Martin (IRL/UAE) 1:13, 14. Romain Bardet (FRA/ALM) 1:27, 20. Philippe Gilbert (BEL/DEC) 2:12