Port Vale boss Micky Adams revealed Ashley Vincent suffered a suspected broken leg in the 2-0 defeat at Bristol Rovers.
Substitute Vincent was hurt as he tried to latch on to an 80th-minute rebound when Lee Hughes' shot was brilliantly saved by Steve Mildenhall.
There did not appear any contact with an opponent, but the 27-year-old striker was stretchered off.
Afterwards Adams said: "It looks like a fractured tibia. We're not sure how Ashley did it and we won't be certain of the damage until we get him checked out, but it doesn't look good."
He added: "I'm concerned about our form because there is a lack of confidence among the players and they are not looking the same as earlier in the season.
"We lost two goals to poor marking at set-pieces, which is always disappointing. But I felt we created the best chances and failed to take them."
Ryan Brunt netted with a downward header after seven minutes and a low near-post shot in the 38th minute as Vale failed to defend two Oliver Norburn corners from the right.
This defeat, their third in four games, means Vale slip to third in the League Two table and they are now just two points above the play-off places.