The early indications from Swansea's medics were that Michu had not suffered ligament damage, but the Spaniard left the Madejski Stadium with his ankle heavily strapped.
Swans manager Michael Laudrup said: "His ankle is twice as big now. We don't know how bad it is. The doctors and the physios say it shouldn't be the ligaments, which is the most important thing."
He added: "The next question is 'will he play on Saturday?' I don't know. We will have to wait 24 hours. Hopefully it is not too bad. It is not a muscle injury but still we have to be careful. He has to be 100%."
Michu limped out of the action after poking a close-range effort over the bar and curling a long range effort just wide as Swansea were frustrated by Reading. Laudrup's men dominated the first half but in the end were left clinging on for a point, with Chico Flores heading Adam Le Fondre's volley over the bar.
"I am satisfied with the performance, not so much the result," Laudrup said. "We dominated for 75 minutes and we could have won the game. The performance was good."
Stopping the rot was vital for Brian McDermott's men, who had come so close to earning a draw against Manchester City before Christmas.
"We need to find a way to get results and today we got a result," McDermott said. "We are disappointed they didn't give us the handball goal because they normally give them here. Adam would have headed it but he said he got pulled back.
"We were much more resilient, it is important to move on with a point and we can look forward with confidence to West Ham.
"We have got a point and a clean sheet and we are off the bottom of the table."