Home favourite Heras is bidding for his fourth title in 2005

The Spaniard needed 15 stitches in his left knee but remounted to finish the stage and stay in second place overall behind Russian Denis Menchov.

Italian Alessandro Petacchi, riding for Fassa Bortolo, won a bunch sprint to take the 148km-stage win.

Second in the stage from Logrono to Burgos was German Erik Zabel with Italian Marco Zanotti third.

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Liberty Seguros media officer Jacinto Vidarte expects Heras to start Friday's stage.

"The team doctors gave him the stitches in the team bus and he's now getting treatment for the wound," he said.

Jacob Piil was also involved in the fall that injured Heras and came off far worse.

After spending a long time motionless on the floor, the Dane was taken away by ambulance but later retured from the race.

Stage 12 results:

1. Alessandro Petacchi (Italy / Fassa Bortolo) 3:13:36
2. Erik Zabel (Germany / T-Mobile) same time
3. Marco Zanotti (Italy / Liquigas)
4. Tom Boonen (Belgium / Quick-Step)
5. Heinrich Haussler (Germany / Gerolsteiner)
6. Jimmy Casper (France / Cofidis)
7. Julian Dean (New Zealand / Credit Agricole)
8. Anthony Geslin (France / Bouygues Telecom)
9. Arnaud Coyot (France / Cofidis)
10. Tom Steels (Belgium / Davitamon - Lotto)

Overall classification:

1. Denis Menchov (Russia / Rabobank) 48:21:11"
2. Roberto Heras (Spain / Liberty Seguros) +47"
3. Francisco Mancebo (Spain / Illes Balears) +1:53"
4. Carlos Sastre (Spain / Team CSC) +1:57"
5. Carlos Garcia Quesada (Spain / Comunidad Valenciana) +3:31"
6. Tom Danielson (United States / Discovery Channel) +5:03"
7. Manuel Beltran (Spain / Discovery Channel) +5:09"
8. Juan Miguel Mercado (Spain / Quick-Step) +5:45"
9. Ruben Plaza (Spain / Comunidad Valenciana) +5:58"
10. Michele Scarponi (Italy / Liberty Seguros) +6:37"