LONDON: Gary Cahill has warned Chelsea cannot afford to allow their season to be affected by the latest off-field controversies to surround the club ahead of their trip to Swansea on Saturday.

The build up to the Premier League leaders' journey to Wales has been overshadowed by Chelsea's decision to lodge a formal complaint against referee Mark Clattenburg, alleging the match official used inappropriate language against midfielder John Obi Mikel during their recent Premier League defeat by Manchester United.

The matter will be investigated by the Football Association and the Metropolitan Police and comes just two weeks after Chelsea captain John Terry was hit with a four-match ban and #220,000 ($355,000) fine after being found guilty of racially abusing QPR's Anton Ferdinand a year after the incident took place.

Chelsea and the police are also undertaking separate investigations into claims a supporter made a racist gesture towards United's Danny Welbeck when the two clubs met for the second time this week.

The Clattenburg investigation in particular could provide a diversion for Cahill and the rest of Roberto di Matteo's squad, some of whom will be interviewed as potential witnesses.

But the centre-back – who has been deputising for Terry – believes Chelsea's success in defeating United 5-4 to reach the quarter-finals of the League Cup three days after the initial loss to Alex Ferguson's side is proof of their ability to remain focused.

“It's important that we don't let anything affect us and we showed that won't happen,” said Cahill. “Whatever is going on off the pitch, players relish playing football.

“I had never felt as angry and disappointed about a game two days later and we really wanted to put that right.

“Although we were very unfortunate in the first game, it was important that we got back to winning ways after two sticky results, especially against Manchester United.”

Chelsea will be anxious to claim three points at the Liberty Stadium after suffering their first league defeat of the season last weekend.

That loss meant their four-point advantage at the top of the table was reduced to just one and a further slip could see them drop down to third place.

Di Matteo will make a number of changes to his midweek starting line-up against a Swansea side who won at Liverpool this week to join Chelsea in the quarter-final draw of the League Cup. Cahill is aware of the strengths of Michael Laudrup's side and the England defender said: “It was a tough game when we went there last season and drew 1-1.

“It is going to be tough again but we have some momentum from Wednesday night and it was important to win after two disappointing games.”

Swansea lost narrowly at champions Manchester City last weekend but Laudrup believes his side – who sit in 11th spot – are now building useful momentum.

“We can compare Saturday's game to the one against Man City,” said the Demmark great. “We know what to expect from them (Chelsea) because they have so much quality, but it is up to us to try and stop them.

“The big teams have to attack, and that can sometimes mean we have more time to play because there are different approaches to these kinds of games.

“But I'm not concerned about Saturday's game because I know we will play well. If I'm honest, I'm more concerned about the next game against Southampton because we play a smaller club on the back of three big games.”

Chico Flores is a doubt for Swansea with a dead leg. – AFP