Story highlights Unsettled Man Utd striker subject of a "written offer" by West London club

Striker played second fiddle to Robin van Persie during 2012/13 season

Rooney reported to be "angry and confused" at treatment by Manchester United

Returning Chelsea boss Jose Mourinho describes offer as "clean" and "ethical"

English Premier League champions Manchester United have rejected a bid for striker Wayne Rooney from rivals Chelsea.

The West London club revealed in a statement released Wednesday that it has submitted a "written offer" for the unsettled striker.

"Chelsea Football Club can confirm that yesterday it made a written offer to Manchester United for the transfer of Wayne Rooney," the Chelsea statement read.

The fee is not known, but reports in the UK media on Wednesday speculated that Chelsea might be offering winger Juan Mata or defender David Luiz plus cash in the return for the services of Rooney. But the club flatly reject the claim.

"Although the terms of the offer are confidential, for avoidance of doubt and contrary to what is currently being briefed to the press in Sydney (where Manchester United are currently on tour), the proposed purchase price does not include the transfer or loan of any players from Chelsea to Manchester United," the Chelsea statement read.

Manchester United have not commented further on the bid.

After overseeing his first game back in charge of Chelsea in Bangkok, Jose Mourinho described the offer as "clean" and "ethical" before adding that the club have not, and will not, bid for any other strikers this summer.

"We love the player, we are interested in the player, we made the bid. We have nothing more to say and nothing more to do. And now we have to respect and be ethical in this process," Mourinho said following Chelsea's 1-0 win over Singha All Stars.

Chelsea's interest in Rooney is the latest twist in a long-running saga about the striker's future.

Rumors of the 27-year-old's discontent began to surface towards the end of last season as Manchester United were romping to a 20th League title.

The club eventually won by 11 points from rivals Manchester City, but Rooney was playing second fiddle to striker Robin van Persie who signed from Arsenal at the beginning of the 2012/13 season.

The Dutchman netted 30 goals in 48 matches for his new club while Rooney only managed 12 from 37.

At the end of last season, outgoing manager Alex Ferguson confirmed that Rooney had submitted a transfer request.

"We refused it. He should go away and think it over. He's not happy being taken off a couple of times this season, but Rooney in top form wouldn't have been taken off," Ferguson said following United's final home game of the season.

Ferguson's replacement, David Moyes tried to quash ongoing rumors when he officially took over the managerial reigns at the club earlier this month.

Wayne is not for sale ," Moyes, who signed a six-year contract to replace Ferguson in May, told reporters. "He is a Manchester United player and will remain a Manchester United player.

"I see a glint in his eye. He looks happy, he looks like he will knuckle down and get himself right."

That apparent glint has been replaced by a furrowed brow with Rooney reported to be "angry and confused" at his treatment by his current employers.

The striker, who joined United from Moyes' previous club Everton for $39 million in 2004, signed a new improved five-year-deal in October 2010 following a similar falling out with the club's management.

Manchester United's chief executive, Ed Woodward recently said that no contract renewals are currently being discussed.

"I am not sitting down with any player on an extension and there is no trigger date in the diary. Would we be afraid to run a contract down? Of course not," Woodward said.