Cole, who made his senior international debut this week against Spain after 10 goals for his club this season, limped off after 34 minutes at Upton Park.

"We don't know how bad it is yet," said Zola. "He is going to have an X-ray in the next 24 hours and hopefully it will be just a twist."

Zola also lost Luis Boa Morte to a hamstring tear and the winger was jeered off by his own supporters when he was replaced just after the break when his side were behind to Stewart Downing's opener.

"As soon as he makes a mistake they pick on him and he doesn't deserve that," Zola said.

Downing's opener came in the 22nd minute, a header from Gary O'Neil's cross after Matthew Upson and James Collins failed to clear.

David Di Michele and Diego Tristan were guilty of missing chances but the hosts eventually drew level.

Savio Nsereko was thrown on by Zola and his free-kick was headed in by Herita Ilunga.

"We had so many chances that I was afraid we weren't going to score," Zola said.

"We didn't deserve to lose and a draw may have been fair. A replay is not great news but we want to go through. It will be tougher but we want to go through."

Zola admitted his side were awful in the first half.

"The first 50 minutes was the worst we have played recently," he said. "It was not near our standards. After that we picked up a bit. You cannot afford not to play high levels.

"It's a good lesson for us. Three months ago we would have lost that game so I am pleased because the players showed we did not want to lose."

Zola is also pleased with the form of Ilunga.

"He has signed a contract for four-and-half years so he will be with us for a long time," Zola said. "I don't think there are many left-backs playing as well he is."

Middlesbrough boss Gareth Southgate added: "It was probably a fair result. I was pleased with how we played, the quality was good and I was pleased how we opened them up. We will take more from it than the result itself."

Southgate felt his side had enough chances to win.

"We got ourselves in enough good situations but that has been the story of the season for us," he said.

"We are at our best when we pass and play football and that's what we were doing today - the players will take great confidence from that.

"A lot of our senior players are coming back, you need them to get results in our league and in this competition.

"It was the best game through this period and the players have the belief that they can turn it around. We know what needs to be done and we believe we can do it."