Louis Van Gaal’s Manchester United side are sitting 13 points below leaders Chelsea in the Premier League standings. (Source: Reuters)

Manchester United manager Louis van Gaal says his expensively assembled squad has not challenged for the Premier League title this season because they do not have a prolific striker like their rivals.

Despite spending more than 150 million pounds ($231.48 million) in the close season, including a six-million pound season-long loan deal for Colombia striker Radamel Falcao, United have looked uncharacteristically subdued when going forward during the campaign.

Van Gaal has come under scrutiny for implementing a number of different formations and playing forward Wayne Rooney in central midfield as United have struggled to keep pace in the title race, with his team in fourth.

The Dutchman claims the club are 13 points adrift of leaders Chelsea and eight behind local rivals Manchester City in second because his strike force have failed to match the scoring exploits of Diego Costa and Sergio Aguero, who have 17 league goals each for their respective teams.

Netherlands captain Robin van Persie is United’s top scorer with 10 league goals, while Rooney and Falcao have struck eight and four respectively.

“We cannot deny that at this moment we don’t have a striker who scores 20 goals in the season,” Van Gaal told reporters ahead of Sunderland’s visit to Old Trafford in the league on Saturday.

“Robin van Persie cannot deny it, Falcao cannot deny it and Rooney — but he is not playing there so much any more.”

United will have to make do without injured Van Persie for Saturday’s match.

Van Gaal sold England striker Danny Welbeck to Arsenal and loaned Mexico’s Javier Hernandez to Real Madrid as part of a summer overhaul after taking over at Old Trafford, putting his faith in 19-year-old James Wilson as the fourth striker.

However, the Dutchman said a lack of goals from the current quartet did not mean he would look for more attacking reinforcements at the end of the season.

“This doesn’t tell anything about next year,” Van Gaal said on Friday.

“They can be having an unlucky year and I have to take account with these aspects and I have to decide, with my staff, if it is these aspects or other aspects.”