Vermaelen, 28, is Arsenal's club captain, but he lost his place in the first XI last season and has been linked with clubs including United and Barcelona.

Wenger confirmed at a press conference that Arsenal had received bids for the left-footed centre-back and when asked which clubs had made them, he replied: "I can't tell you that, but you will know very soon."

Pressed as to whether United were one of the clubs to have expressed an interest, he said: "I think they could be in the group."

While Wenger would not comment on press reports that Arsenal are asking for a fee of up to �15 million ($25.3 million, 18.9 million euros) for Vermaelen, he conceded that he was considering letting him leave.

"It could happen," said the Frenchman, whose side face Manchester City in the Community Shield at Wembley on Sunday.

"I've said since the start of pre-season that it could happen that Thomas leaves us because he needs to play now.

"He had an outstanding attitude and behaviour, but he's in a position where it's difficult to stand in his way if he finds an interesting opportunity."

Wenger confirmed that there were foreign teams among the clubs to have made enquiries about Vermaelen.

When he was asked if he would prefer to sell him to an overseas club, he replied: "Ideally, yes."

Arsenal have been strongly linked with a move for Real Madrid's Sami Khedira, but Wenger said that his squad was already sufficiently well-stocked in central midfield.

- 'Cannot give you names' -

"I don't know who has put him on the market. Is it his agent, or somebody else? I don't know. Is it the press?" said Wenger of Khedira, who tasted World Cup glory with Germany in Brazil.

"But we were never close to signing him. Jack Wilshere has come back fit and in midfield we have quite a few offensive midfielders or box-to-box players."

Wenger was also evasive when invited to discuss reports that he has expressed an interest in signing Liverpool centre-back Daniel Agger.

"I cannot give you any names specifically on who will join us at the moment," he said.

"We are not close to signing anybody and it would be the wrong information."

Wenger has brought four new players to the club during the close season in Alexis Sanchez, Mathieu Debuchy, Calum Chambers and David Ospina.

He said that he was open to making further signings, but emphasised that he already has a large group of players to work with.

"We have still three and a half weeks before the transfer market is closed. I am open to it," he said.

"But it has to be a player who can strengthen our squad. Let's not forget we have Joel Campbell who has come back (from a loan spell), plus the addition of the three others players: Debuchy, Chambers and Sanchez, who have joined us.

"We have already bought four players. We have not lost players until now. We have a big squad at the moment."

Arsenal open their Premier League campaign at home to Crystal Palace on August 16.