As reports emerge that a deal for Brazilian Lucas Moura could yet be reignited, Manchester United manager Sir Alex Ferguson has reiterated that efforts are ongoing to bolster the ranks at Old Trafford.

United have already signed Shinji Kagawa and Nick Powell this summer, with the former starring with the only goal against Shanghai Shenhua on Wednesday.

"We've been trying all summer to add to our squad," said Ferguson, according to Manchester United's website.

"We've got Kagawa and Powell and we're working on one or two other things. I have nothing to tell you in terms of confirmation as to whether any other players are joining us at this moment in time. But we are trying to add to our squad."

Though he didn't mention names, Ferguson has admitted that the club were interested in 19-year-old Lucas. A deal had appeared dead when Lucas' agent claimed that his client would be remaining in Brazil after United's latest offer had been rejected last week.

But Sao Paulo vice president Joao Paulo de Jesus Lopes did not rule out the possibility of talks continuing with United.

"I don't rule out the possibility that in the future we open negotiations with Manchester United as we received them with great courtesy," he told Radio Estadao ESPN.

"And there is the possibility they come back with another offer. Their approach was serious. Other teams have also expressed interest for Lucas, but only through the press from their countries."

As well as Lucas, United have also bid for Arsenal captain Robin van Persie in recent weeks. The Red Devils are reported to have had a £10 million offer for the Dutchman rejected, according to the Daily Telegraph, with Arsenal thought to be holding out for at least £25 million. Despite the fact that Van Persie has just a year remaining on his contract, United surely knew that their bid would be rejected, making it likely that further offers will be forthcoming.

However, Arsenal have reiterated that they will not let the soon-to-be-29 year-old leave for anything less than what they see as the player's true value.

"He is a world class player and we do not want to give him away," said chairman Peter Hill-Wood, according to Sky Sports. "If he is determined to leave then that is up to him, but giving him away is not on our agenda."

Juventus and Manchester City have also made bids for Van Persie.

Manchester United are also thought to be trying to add a midfielder to their squad this summer. There has been further speculation about two names strongly linked to fill that void at Old Trafford: Axel Witsel and Joao Moutinho.

Witsel, 23, impressed in his first season with Lisbon giants Benfica and has reportedly attracted the interest of several European giants, including Chelsea and Real Madrid, as well as United. Any club who want to sign the Belgium international will have to pay up his £31 million release clause, according to Benfica president Luis Filipe Vieira.

"Every club knows what his release clause is," Vieira said, according to Sky Sports.

"If they come here and pay that fee, then there is nothing that we can do.

"We are very happy with Witsel and we do not think about selling him."

United look likely to encounter similar resistance from another Portuguese club in their pursuit of Porto's Moutinho. United were reported by the Times to have made a bid for the 26-year-old Portuguese international earlier in the summer, with Tottenham also said to be keen.

But Porto coach Vitor Pereira has said that the club is not planning on sanctioning the sale of either Moutinho or his coveted teammate Hulk.

"Hulk and Joao Moutinho are both in my plans for next season," he revealed, according to Sky Sports.

"They are our players and are very important to the structure of this team.

"I am not preoccupied by the possibility of big offers from England