Costa thudded into the foot of the post and left the field on 84 minutes to go directly to hospital with what looked like a considerable gash on his shin.
Atletico Madrid moved a step closer to a first La Liga title in almost two decades when Diego Godin and Costa scored to stretched their advantage at the top to three points.
Costa's collision with the post left the striker with a horrible gash to his leg - one which could make him a major doubt for Atletico going forward.
He had a penalty saved at Getafe's Coliseum stadium in the Madrid suburbs shortly before Adrian sent a low cross trundling towards the far post in the 84th minute.
It looked like the Brazil-born forward would not reach the ball before it rolled out of play, but he flung himself full stretch to divert it over the line, colliding heavily with a post and opening a deep cut just below his left knee.
With Costa carried off on a stretcher in apparent agony, there were fears the forward could miss significant playing time but Atletico said he sustained nothing more serious than a cut.
The gash to his shin should not prevent him from playing in Friday's La Liga match at home to Elche.
However, initial reports suggested that the injury may not as serious as first feared, with a representative of Atleti tweeting positive news.
Diego Simeone's press guy, @Pepepasques just tweeted about Diego Costa injury: "Relax people! Everything's fine. Just need to fix the post."
The surprise leaders ahead of much wealthier rivals Real Madrid and Barcelona, Atletico are well placed with five games left to become the first club other than the big two to win Spain's domestic league since Valencia in 2004.
Barca surrendered second place to Real on Saturday when they followed up Wednesday's Champions League elimination at the hands of Atletico with a shock 1-0 defeat at Granada and Real thumped Almeria 4-0 at the Bernabeu.
Atletico have 82 points, with Real in second on 79 and Barca, who host Atletico on the final day of the season, on 78.
Atletico showed no sign of fatigue at Getafe's Coliseum stadium following their exertions against Barca, when they reached the last four of Europe's elite club competition for the first time since 1974.
They last won La Liga in 1996 with a team featuring current coach Diego Simeone in midfield and remain on course for what would be a remarkable double of La Liga and Champions League.
Centre back Godin, who earlier went close with another header, nodded into an empty net five minutes before half-time after Getafe goalkeeper Jordi Codina came out to meet a Juanfran cross but failed to connect.
Angel Lafita was sent off for hauling Miranda down in the penalty area but Atletico's top scorer Diego Costa, back in the side after injury, had his 66th-minute spot kick saved by Codina.
Costa slid in to divert an Adriano cross into the net six minutes from time but had to be carried off the pitch on a stretcher after crashing into a post and opening what looked like a deep gash in his left leg.
- Sports & Recreation
- Atletico Madrid
- La Liga
- Diego Godin