The King Charles spaniel was found on the A38 near Kennford service station in Devon on Thursday afternoon.
The owners of the dog, which suffered two suspected broken legs, have now been traced.
CCTV footage is being reviewed  by police "to shed light" on the incident.
Devon and Cornwall Police said: "We are currently working under the impression that the dog had escaped from its home and ran across the road and sustained its injuries this way."

The South African struck 24 boundaries, sharing century partnerships with Luke Wright (60) and Ben Brown (67), as Sussex moved their score on from 74-1.
Jofra Archer then smashed four sixes and three fours to score 42 off 14 balls as Sussex declared on 443-6.
Leicestershire openers Paul Horton and Arun Harinath reached stumps unbeaten, leaving 389 runs to score on day four.
An injured dog which was first thought to have been thrown from a car on a busy dual carriageway had probably escaped from home and run across the road, police say.
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Sussex's Stiaan van Zyl scored an unbeaten 166 as Leicestershire ended day three 36-0 chasing 425 to win.