Arsene Wenger warned Jose Mourinho that just one defeat could undermine Chelsea's entire season as he refused to give up on the title - or the FA Cup.

Wenger quoted three examples of clubs who had squandered leads in the Premiership - Newcastle in 1996, Manchester United in 1998 and Arsenal themselves in 2003.

He also cited Arsenal's own defeat at Old Trafford last October, when they dropped four points in their next two league games, as proof of how quickly fortunes can change.

The Arsenal boss may seem to be rather clutching at straws, given that Chelsea have a 10-point lead and show no signs of vulnerability.

Indeed, he even joked that he could not rely on the power of prayer as "I can stay up all night and pray 'please God, make Chelsea lose' but it won't make them lose."

However, without revealing any specifics, he claimed to have spotted flaws in the Blues' game which could yet prove their undoing.

Wenger said: "There are signs that can give us hope. First of all, the quality of our own game. Secondly, other signs that are very interesting to analyse.

"What are they? I will keep that for myself. But at the moment you cannot ask me to give up on any pretension to fight or to come back."

Chelsea may have lost just once in the league all season, recovering immediately after that setback at Manchester City.

"At the moment, Chelsea do not look vulnerable but if you lose one or maybe two games, then you can look super-vulnerable. There is always a weakness, no matter how you play football."

Arsenal can, however, only look to their own performances and even though they face United next Tuesday, Wenger will not rest his key players against Wolves in today's FA Cup fourth round tie.

While Dennis Bergkamp may be given a breather, Thierry Henry and Patrick Vieira will both start against the Championship side as Wenger aims for the confidence boost of a healthy victory.

Wenger also vowed to ensure that Arsenal do not compromise on their attacking style in a thinly-veiled comparison with Chelsea.

"We have scored 49 league goals from open play this season and the second team behind us is Middlesbrough with 29," he said. "We just have to keep going as we have a vision of the game, where we do not have to consider anybody else.

"I don't go along with those who say the only realistic chance of Arsenal winning something this season is in the FA Cup.

"I feel the pride and the professionalism of everybody here as a winner will make us fight even when things look desperate. If we play a game of quality, we will win matches. And if Chelsea drop points, we've still got a chance."

Meanwhile, Alex Ferguson has once again backed under-fire Tim Howard over the goal that cost Manchester United a place in the League Cup final. But his soothing words may not be enough to earn the American an FA Cup starting slot against Middlesbrough today.

While most pundits blamed the United goalkeeper for allowing Damien Duff's touchline free-kick to bounce in against Chelsea on Wednesday, Ferguson's immediate reaction was to point the finger at his defence.

Ferguson is sticking to his initial view and claimed Howard was blameless for defeat in a contest he felt his team were controlling.

"It was not Tim," said Ferguson. "There is no doubt it was the defenders' fault. The players know. They can hold their hands up quite easily because they know it was their fault.

"The result is there now but the thing that bothers me is we had the game by the throat and then got kicked in the teeth by a 45-yard free-kick."

Despite his exoneration of Howard, the indications are Roy Carroll will return to face Middlesbrough at Old Trafford.

With Alan Smith's injured ankle unlikely to be risked ahead of next week's Premiership showdown with Arsenal, Wayne Rooney is set to return, possibly at the expense of Ryan Giggs, who may also be rested for the Highbury trip.

Phil Neville is also pushing for a recall after sitting out the last two games and after his recent run at right-back, may fill the central midfield slot as skipper Roy Keane misses out through suspension.

On strict form lines, United should emerge victorious with something to spare having beaten the Teessiders in relative comfort at the Riverside on New Year's Day.

That ignores Steve McClaren's impressive record at Old Trafford since quitting as Ferguson's assistant in 2001. On his four return trips to his old club, he has won twice and his team also had much the better of this season's 1-1 draw when it took a late Smith effort to salvage a point for the hosts.

In addition, Boro dumped United out of the FA Cup at this stage in 2002.

After enjoying a week free of competitive action, Ferguson knows his former number two is quite capable of inflicting more misery on the Red Devils faithful unless his team are fully focused on the job in hand.