London - Arsene Wenger admits a reunion with old rival Sam Allardyce could pose serious danger to Arsenal's hopes of rekindling their title challenge when Crystal Palace visit the Emirates Stadium on Sunday.
Wenger has traded barbs with Allardyce numerous times in the past and the sight of the Palace boss glowering down the other end of the touchline might give the Arsenal manager a pang or two of concern this weekend.
With fourth placed Arsenal battling to avoid being cast adrift in the Premier League title race, the last thing Wenger needs is to see his side roughed up by the latest team to turn to former Bolton and West Ham boss Allardyce in a bid to stave off relegation.
Allardyce will be in charge of Palace for just the second time since replacing the sacked Alan Pardew, but his first match -- a gritty 1-1 draw at Watford on Boxing Day -- suggests the Eagles, languishing in 17th place, are already adapting to their new manager's desire for a direct style and physical approach.
Having narrowly beaten West Bromwich Albion with a late goal on Monday after losing to Everton and Manchester City, Arsenal could do with an uplifting performance to offer hope of better things to come in 2017.
But Wenger knows Allardyce, aiming to restore his reputation after the embarrassing end to his 67-day reign as England manager, will send out a motivated group determined to upset the odds with their first victory at Arsenal since 1994.
"It has become vital for everybody to stay in the league," Wenger said.
"It has become an extremely big problem for everybody and when teams look for managers he was one out there who had the experience and the quality.
"The level of confidence or the level of urgency always goes a bit up when a new manager comes in, of course. That makes the game more difficult.
"When you look at their squad, it's a talented squad, because they have potential going forward, they are quick on the break and they are very versatile.
"They have experience, they have technical quality. It's a team that can be dangerous for everybody."
Trailing leaders Chelsea by nine points, Arsenal have no margin for error, but Wenger believes it is still possible to overhaul the team he claims are title favourites.
"At the moment Chelsea are the super-favourites," he said.
"But it is theirs to lose as we say here in England. They can still lose it, at the moment they have won it but they can still lose it."
Arsenal are likely to be without Theo Walcott on New Year's Day as the England winger is still working his way back from a calf problem.
Kieran Gibbs is out with a knee injury, while Shkodran Mustafi is available following a hamstring problem.
Wenger also has a decision to make on when to reintroduce Danny Welbeck after the England forward returned to training following a second serious knee injury in the last two years.
"He's fit, he's sharp," Wenger said. "Will I involve him in the short term or not or will I play him first in a game with the under-23s?
"I have not decided yet, but in training he looks quite good."
Palace defender Damien Delaney is suspended and could be replaced by James Tomkins, who returns after a thigh injury.
Eagles midfielders James McArthur and Joe Ledley are also back in contention.