In a match dominated by a waterlogged pitch which made football impossible, the Portuguese superstar was caught by an elbow from Levante defender David Navarro in the third minute.
He soldiered on, giving Madrid the lead, before being taken off at half-time.
"He's dizzy. In the first half he was unable to see properly with that eye, but during the break he couldn't see properly with either. So it was impossible for him to continue," said Madrid boss Jose Mourinho.
"When he gets to Madrid he'll go to hospital to have the tests he needs."
Levante levelled through Angel Rodriguez in the 62nd minute but Madrid won it when Xabi Alonso, who had earlier missed a penalty, delivered a free-kick for young substitute Alvaro Morata to head a late winner.
Mourinho was delighted with his players' character in testing circumstances.
He added on www.realmadrid.com: "It was a difficult match for everyone.
"We have adapted to the conditions and it was an honest fight between two honest teams that have given their all in search of the result.
"The team has had to play with great character and strength and we deserved to win. I hadn't won here before and they are three extremely important points."
Mourinho recently criticised Alberto Toril, the boss of reserve team Castilla, who play in the Segunda Division, and accused him of prioritising results ahead of the development of young players.
And the former Porto, Chelsea and Inter Milan boss was taking the credit for the promotion of match-winner Morata.
"My praise comes from helping him grow, training him and not letting him go to another team like (Juan) Mata or (Alvaro) Negredo," he said.
"I brought him into the first team, no-one else. I brought him for three successive seasons.
"I told the club to give him a first-team contract and to not let him leave this year.
"We have (Gonzalo) Higuaín and (Karim) Benzema and when they don't play Morata will.
"What others say for me doesn't matter, what's important is that he's growing as a player and as a person because his life is changing by becoming part of the first team.
"Morata is very stable mentally and I hope that remains the case after he has read what will be published in the days to come."
Morata was quick to return the praise and thanked Mourinho for believing in him.
"I had some offers to leave Madrid but the coach told me he was counting on me and that I should stay," he said.
"I am at the best club and under the best coach in the world, I will make progress step by step.
"Mourinho gives me advice and helps me, I am trying to take it all in to become a better player.
"I am calm because I know that if I do as he says things will go well for me."