Nani was far from impressive in his only start so far this season, against Everton. Reuters

The transfer window may now be shut, but speculation continues about Manchester United's interest in two leading international forwards. United were linked to Poland's Robert Lewandowski and Brazil striker Leandro Damiao over the summer and both have been commenting on their futures.

Lewandowski struck 22 goals as Borussia Dortmund retained their Bundesliga crown last season before going on to score the opening goal for his country at Euro 2012. With the 24-year-old having less than two years remaining on his contract, both Manchester United and Chelsea were thought to have made approaches for him during the close season.

Dortmund, however, claimed that the striker's representatives were trying to talk up the possibility of Lewandowski leaving the Westfalenstadion. Talking to German newspaper Bild, Lewandowski has suggested that he could be on the move next summer.

"I don't set myself any limits. I don't know what will be after this season," he said, according to the Daily Mail.

"I can't and don't want to rule out anything. This would not be professional."

Lewandowski went onto say that he has no immediate plans to extend his deal, which will potentially compel Dortmund to cash in on him at the end of the season.

"I have another two years on my contract. This is a long time. I don't have to decide today if I extend it or not. But, like I said, I only concentrate on Borussia right now."

Despite spending big on former Arsenal forward Robin van Persie, United are also thought to be keen on Internacional star Damiao. Earlier this week the Daily Mail claimed that United had already discussed signing the 23-year-old in January.

Tottenham are also long-term admirers of the top scorer in the recent Olympic Games and Damiao has revealed that a large offer was made for his services this summer.

"The value of the offer was very good for me and for Internacional," he said, according to Sky Sports.

"But it didn't happen. I think Giovanni Luigi is a great president and he knows what he's doing.

"I'm very happy to be playing in Brazil. I'll certainly leave at some point for sure, but not today."

Damiao has established himself as the leading striker for Brazil and has also been linked with Liverpool, as well as Inter Milan and Real Madrid. Continued reports of United's interest in either Damiao or Lewandowski is likely to fuel rumors about Wayne Rooney's future at Old Trafford.

Further speculation has also emerged about the future of Manchester United winger Nani. The Daily Mail claims that Zenit St Petersburg are still looking to complete a £25 million move for the Portuguese winger before the close of the Russian transfer window on Thursday.

The25-year-old has so far failed to sign a new contract at Old Trafford, leading to reports throughout the summer that the club would look to cash-in on the former Sporting Lisbon player. Nani could also find himself down the pecking order at United this season following the arrival of Shinji Kagawa and Van Persie. After starting the opening match of the season against Everton, he was left out of the squad against Fulham before appearing as a substitute against Southampton.

Despite spending a combined €80 million (£63.5m) in the past week on Hulk and Axel Witsel, Zenit claim to still be interested in both Nani and Porto midfielder Joao Moutinho.

"It's true we are negotiating for Nani and Moutinho, but Hulk and Witsel were our top priorities," said Zenit general director Maxim Mitrofanov, according to the Daily Mail.