Sir Alex Ferguson believes Serbian winger Zoran Tosic can make an impact at Manchester United this season after wrapping up a double deal for the 21-year-old and his Partizan Belgrade team-mate Adem Ljajic on Friday.

United revealed late last year that they had reached agreement with Partizan to sign the duo in a transfer thought to be worth around 17 million pounds (17.6 million euros) and the Premier League champions have now concluded contract negotiations with both players.

Tosic, capped 12 times by Serbia, will link up with United immediately while 17-year-old striker Ljajic will spend the rest of the season on loan at Partizan.

But although Tosic will be ineligible for Sunday’s FA Cup third round tie at Southampton, United manager Ferguson is confident that the left winger will quickly challenge for a place in his starting line-up at Old Trafford.

Ferguson said: “We have been watching Tosic for over a year and in that time, he has become a regular in the Serbia national team.

“He’s a winger and we like wide players here at Manchester United, so we are very hopeful that he will do well for us.

“He hasn’t played since December 10, however, so he will need some time to adjust to the speed of the game over here and get used to the training.

“But once he gets himself accustomed to the pace, then I am sure he will play a part for us this season. Ljajic is another good player with real quality and he will come over to Manchester in time for next season.

“That is it for Manchester United in this transfer window, though. We are done now with our business for this season.”

Ferguson is likely to make a series of changes for the trip to the south coast for Sunday’s repeat of the 1976 FA Cup Final against Championship strugglers Southampton.

Cristiano Ronaldo is set to be rested, while Carlos Tevez is not due back from attending family business in Argentina until Sunday evening.

Despite reports suggesting that Tevez is close to signing a permanent deal at Old Trafford, Ferguson insists that the club are no closer to thrashing out an agreement with the player’s representatives, who continue to own the Argentinian.

Ferguson said: “I’m not going on about the Tevez contract because it is never-ending. Chief executive David Gill is dealing with it, but there is nothing to report.”

The FA Cup clash starts a busy January for United, who also have a Premier League clash at home to Chelsea on Jan 11 in-between a two-legged League Cup semi-final against Championship club Derby County.

And England defender Rio Ferdinand, who will miss the Southampton game, is facing a battle to fit for the Chelsea clash after being laid low with a back injury since pulling up in the pre-match warm-up at Stoke on December 26.

Ferguson said: “Rio is still not training because we need to give his back the time to settle. It has happened a few times now, but he is tall, with a long back, so it can happen.

“He definitely won’t be involved against Southampton or Derby, but we hope he will be back for the big one against Chelsea.”

Partizan Belgrade have insisted they have not had any contact with Manchester United over Zoran Tosic or Adem Ljajic.

United are believed to be looking at both players with reports suggesting they have already agreed terms for Tosic which could also see Ljajic moving to Manchester.

Tosic is a current Serbian international and reports in England have claimed that Sir Alex Ferguson will be part of a United delegation that will attend a work-permit hearing this week over the left-winger.

The 21-year-old does not meet current work-permit criteria to play in the Premier League but, given he is valued at £8million, reports suggest United are trying to broker a permit for him.

However, Partizan sports director Ivan Tomic has stated that United have not signed either player, amid claims the European champions will try and strike a double deal.

United’s interest in Ljajic - another attacking midfielder - heralds from the fact he was on trial at Old Trafford earlier this season.

The 17-year-old is understood to have impressed, which has led to constant speculation that a move to United was in the pipeline.

“It is not true that Tosic and Ljajic have already signed for Manchester United,” Tomic said.

“It is simple, there has been no direct contact or official offer coming from England.

“Of course, it would be nice if they want some of our players, but it’s not true.”

Tosic has also continued to insist he knows nothing about a deal.

“I have nothing new to add on that subject, as I contacted my managers and they told me to keep my focus on playing and to stick to our mutual agreement which is that they will not inform me about anything until things move on to a much clearer situation,” Tosic told Vecernje Novosti.