Jose Mourinho wants to add two forwards to his Manchester United squad during the summer transfer window, sources have told ESPN FC, due to concerns over the ability of his current strikers to make the team competitive in every competition.

The United manager admitted earlier this week that he has already identified targets for the summer and sources said that Mourinho has made it clear that he needs two proven goal scorers.

Atletico Madrid forward Antoine Griezmann is United's No. 1 target and Mourinho is confident that the club's spending power and ambition has put them in pole position to sign the Frenchman -- potentially for a world record fee in excess of the £89.3 million paid for Juventus midfielder Paul Pogba last summer.

But with United scoring just 33 goals in 23 Premier League games so far this season, Mourinho has become alarmed by the lack of potency from his current forwards and has accepted that a second attacking addition will be required in the summer.

Tottenham's Harry Kane would be United's ideal summer signing, but senior figures at Old Trafford have no expectation of the 23-year-old being allowed to leave White Hart Lane or, indeed, that he would consider a move away from the club.

Antoine Griezmann is the club's No. 1 target this summer. Power Sport Images/Getty Images

Mourinho has always built his successful teams around powerful and quick centre-forwards, with the likes of Benni McCarthy, Didier Drogba, Diego Milito and Diego Costa all proving key players under the Portuguese coach. And with efforts already being made to sign Griezmann, United's scouts have now been tasked with finding a striker capable of emulating the success of Mourinho's previous centre-forwards.

The former Chelsea manager brought in Zlatan Ibrahimovic on a free transfer from Paris Saint-Germain last summer, despite the Swede approaching his 35th birthday, because of concerns that neither Anthony Martial nor Marcus Rashford possessed the necessary experience to act as the focal point of United's attack.

Mourinho's fears have subsequently been borne out, with Martial scoring just six goals in 22 games and Rashford scoring the same number, having made six more first-team appearances.

Ibrahimovic has proven to be a huge success, scoring 19 goals in 31 games, but Mourinho accepts that he cannot rely on the former Barcelona and Juventus forward to be as productive next season and that there is a crucial need for two new forwards in their prime, rather than players at the beginning or end of their careers.

Wayne Rooney's poor return of just five goals in 28 appearances has been a surprise to Mourinho and, with the 31-year-old record scorer no longer able to claim a regular first-team spot, there is an increasing likelihood of him being allowed to leave Old Trafford this summer.