Alex Ferguson admits Manchester United may struggle to compete with Chelsea and Manchester City in the transfer market

United manager predicts a busy summer of activity

Sir Alex Ferguson has admitted that Manchester United lack the spending power of Chelsea and Manchester City.

Yet the newly crowned champions will be "competitive" in this summer's transfer market in what Ferguson expects to be a busy summer of activity.

Manchester United have been strongly linked with a move for Borussia Dortmund front man Robert Lewandowski, while there remains uncertainty over the future of Wayne Rooney, despite assertions from the club that the England striker will remain at Old Trafford.

Any attempts to bolster this season's Premier League winners is likely to face stiff competition - particularly from Chelsea and Manchester City.

With Chelsea set to install a new manager over the summer, quite possibly Jose Mourinho, the west London club are likely to reshape their team in the manager's image. Radamel Falcao has already been linked while a £20m deal for Andre Schurrle has practically been agreed.

Meanwhile, having put up a pitiful defence of their Premier League crown, Manchester City are sure to be on the look out for new star names for the Etihad Stadium. Mario Balotelli, who left for AC Milan in January, has not been replaced while the club have been severely punished for their failure to outmaneuver Manchester United when Robin van Persie was available last summer.

Ferguson concedes that going head-to-head with those two clubs on finances alone may prove problematic.

"We're competitive in the market - we're not Chelsea or Manchester City in terms of money but we're competitive," Ferguson told Inside United.

Despite that, United have already been making moves. England Under-21 wide-man Wilfried Zaha was signed from Crystal Palace in January, then immediately loaned back to the Championship outfit for the remainder of the campaign.

A midfielder and a left back are the other positions understood to have been targeted by United - with Ferguson a long-term admirer of Everton's Leighton Baines.

"We've been doing a bit of work over the last three or four months, targeting who the players are that we feel could enhance us, make us better or help us maintain the level we're at," revealed Ferguson.

"Hopefully the players we bring into the club in the next year or so will be of the quality we need."