Although Ferguson is not keen to sell him, he will listen to any interest from other clubs and will allow Kleberson to move if it is in the best interests of the player.
United would have to take significant losses on both, given the depressed state of the transfer market. Forlan arrived in January 2002 for £7.5m and Kleberson joined United last summer for £5m.
There is no guarantee that United will be able to sell the players but if they are able to do business it would trim the club's wage bill.
Forlan is earning about £1.5m a year and despite a modest return of 17 goals - 10 in the Premiership - that would rise to nearer £2m a year if he were still around next season.
Kleberson, meanwhile, is earning a similar amount after arriving from Paranaense last summer. United supporters will be surprised to learn that Kleberson may be sold, but less so Forlan.
The striker seemed to be heading for Middlesbrough from Argentinian club Independiente when Ferguson stepped in and offered him the opportunity of partnering the prolific Ruud van Nistelrooy at Old Trafford.
Despite sporadic flashes of ability and the occasional spectacular goal, Forlan has never looked the part. The player is aware that time may be running out and it is understood he would not be opposed to a move.
Sources close to Forlan indicated he began to realise that his time may be up when Ferguson did not include him in his plans for the recent FA Cup semi-final triumph over Arsenal at Villa Park.
Ferguson prevented a clutch of players joining their countries for internationals in the week before that game but he allowed Forlan to head off to South America to team up with Uruguay.
Even when it later transpired that Van Nistelrooy was unfit to face Arsenal and fellow striker Louis Saha was cup-tied, Ferguson made no attempt to change Forlan's plans to arrive back in England at 5.30pm the evening before the game.
Forlan watched from the stand as a makeshift attack of Ole Gunnar Solskjaer and Ryan Giggs propelled United into the FA Cup Final.
They will be led out in the Cardiff showpiece by Roy Keane and last night Ferguson shed more light on his captain's decision to resume his international career with the Republic of Ireland.
Keane announced on Tuesday that he was ready to play for his country again but Ferguson has revealed that he is only likely to play in competitive games as the Republic attempt to qualify for the 2006 World Cup in Germany.
Ferguson said: 'This might be the thing that will drive him on for the next two years.
'It will only be five competitive matches each year. That is what will happen, I think.'
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