The right-back sustained a tear in the medial ligament of his right knee during our 1-0 victory over Aston Villa.

Johnson will see another specialist before a timescale is put on his recovery.

But Benitez told Liverpoolfc.tv: "Johnson has a problem, so he'll see a specialist and then we'll talk but we know he'll be out for at least one month. But we are waiting for another opinion and then we'll know how long."

Meanwhile, Benitez is hopeful of having Albert Riera back within a week following a knock sustained versus Blackburn - though Martin Kelly and Nabil El Zhar may yet be out for another fortnight.

"Kelly and Nabil still need maybe one or two weeks," said Benitez. "Riera will start training tomorrow, so hopefully in the next week he can be available."

The third round tie is sandwiched between crucial fixtures with Aston Villa and Tottenham, but Benitez knows the Cup is perhaps our best chance of silverware in 2009-10.

He told Liverpoolfc.tv: "It's always been important but you know that when you're out of the Champions League, the people think about silverware and the FA Cup is very, very important for us.

"We want to progress, we want to go as far as we can.

"We'll have to analyse and consider what to do and we still have another training session. We'll see how the players are but maybe we won't change too many.

"We know we're playing against Tottenham eight days later, so we'll have time. We can put a strong team out.

"Always in the FA Cup it's really important to do things right. Everyone wants to win and it's a massive competition, so we have to be ready."

Meanwhile, Benitez is not ruling out some transfer activity over the coming month.

Liverpool could do business when the transfer window opens on January 1, though the gaffer insists it is not easy to buy top-class players midway through the season.

He said: "We are working hard and trying to do our jobs, and we'll see if we can do something.

"We are looking in the market but it's not easy to find good players available because the majority of them are playing in top sides.

"But we are trying to find solutions if we can.

"We have some good players who people are interested in because they're not playing too many games, but we have to manage carefully."

Liverpool signed off an up and down 2009 with a fantastic win at Villa Park.

Asked if he would start 2010 by making some New Year's resolutions, Benitez said: "The main thing for me is to wish health to everyone. After this, it's for us to win trophies, to improve and to do well. Hopefully we can win some silverware in the next year."