Stewart Downing lasted just 25 minutes of Liverpool's 0-0 draw at home to West Ham on Sunday because of illness, manager Brendan Rodgers has revealed.
The winger declared himself fit for the Premier League clash despite feeling unwell on Saturday.
But he was soon unable to continue, and Rodgers replaced him with Daniel Sturridge, who later had a goal ruled out for offside.
Downing should be available for next Saturday's trip to Reading, with Rodgers telling the Liverpool Echo: "He took ill, but he wanted to give it a go. He's in good form at the moment.
"He took some tablets but when he was out there, he was very weak. When he came off, you could see it in him that he wasn't feeling well."
Rodgers admitted to his frustration after Liverpool failed to make a breakthrough against the Hammers.
Sunday's draw has left his side in seventh place with six games to go, and with their chances of European qualification looking slim.
Liverpool are seven points adrift of fifth spot, which is where they would need to finish to guarantee a place in next season's Europa League.
"We are very frustrated," Rodgers said. "Obviously we didn't get the three points I thought we were more than deserving of. We kept pushing from the very first minute.
"I thought the intent in our game was very good, some of our quality arrived in good areas."