London  - Liverpool manager Rafael Benitez will have to prove his worth this week as Liverpool go into what could be a pivotal week in their season.

The Spaniard's side lost their fourth league match of the season at the weekend and have to play champions Manchester United on Sunday in a game that could go a long way to deciding if they will be contenders for their first title since 1990.

Before that, though, they have to take on talented French side Lyon at Anfield on Tuesday night in their latest Champions League clash, knowing that a defeat would leave them facing an uphill battle to qualify for the knockout stages.

The Reds won their opening group match against Hungary's Debrecen, but were well beaten last time out against Fiorentina in Italy, going down 2-0.

To compound matters, injuries to key players - Steven Gerrard and Fernando Torres are both doubtful starters on Tuesday - have left them short of world class performers, and, having lost two successive league matches they are in danger of losing their way.

Captain Jamie Carragher admitted that their losses, the latest in Sunderland coming in bizarre fashion when the ball bounced into the net off a beach ball lying in the penalty area, were frustrating.

But Carragher said they would be doing everything to cut out the uncharacteristic defensive errors that have cost them games this season.

"We will stick together and work hard on the training ground to put things right," the defender said. "We know we've got a good team, good players and a good manager so we've got to have belief in ourselves and keep going.

"We have the quality and the belief we will get back to winning ways soon, hopefully starting on Tuesday against Lyon."

Benitez said his side's fourth league defeat was disappointing but not necessarily fatal in a season where the likes of Manchester City and Aston Villa have made strong starts, with many feeling they could make a realistic title challenge and be real competition for the so-called big four of United, Liverpool, Chelsea and Arsenal.

"In a normal season teams at the top would be winning every game and it would be a long distance to the top now but Chelsea have lost two games and I think we'll see a lot of top teams lose games," Benitez said.

"Losing four games is bad but crucial? That depends on the next few games. If we can win two or three games in a row we can be at the top of the table. It's a question of keeping our confidence, working hard and trying to do better.

"We have an important game on Tuesday and then on Sunday. It's not important to talk about the table, we just have to think about getting three points in every game.

"You have to analyse some things. We made some mistakes and we need to find solutions. We won five or six games in a row, so I think we were fixing things, but in these difficult games we need to improve."

Gerrard and Torres will have late fitness tests after missing the weekend defeat at Sunderland.

But Javier Mascherano should start after he was left on the bench at the Stadium of Light after a long trip back from captaining Argentina as they won in Uruguay to secure qualification for next summer's World Cup finals. (dpa)