Manchester United have completed the signings of Zoran Tosic and Adem Ljajic, the two Serbian youngsters, in a combined £16.3million deal from Partizan Belgrade.

The move was thrown into doubt last month because of Tosic’s wage demands and the number of agents trying to get involved in the transfer, prompting reports that Arsenal or Manchester City could hijack the deal. However, the 21-year-old winger will join United next week with Ljajic, an under-21 international, staying in Belgrade for the remainder of the season.

Sir Alex Ferguson, the United manager, who made a personal plea on Tosic’s behalf at his work-permit hearing in Sheffield, regards the pair as players of outstanding potential, with Tosic, a full international, regarded as a potential long-term successor to Ryan Giggs. Under the terms of the deal, United have agreed to pay Partizan a maximum of £16.3m if the players meet certain pre-identified targets, but the up-front payments will be considerably smaller.

Ferguson confirmed that Tosic and Ljajic will be United’s only acquisitions during the transfer window, with the future of Carlos Tévez unlikely to be resolved until the summer. "That is the end of the transfer business at Manchester United this year," he said. "There will definitely not be anything else this January."

The United manager has not ruled out Tosic making a first-team appearance this season. "We have watched him for over a year," Ferguson said. "Hopefully he does well but we will have to give him time because he has not played since December 10. He will need to get used to the tempo of our game and the training but he could play."

Ferguson confirmed he expects Nemanja Vidic to play the role of father figure, which the Serbia defender is happy to take on. "It is good for Serbia and for me to have them around," Vidic said. "I hope they enjoy it."

Vidic took the pair out for dinner before they finally signed their contracts, although the pair took no persuading. "I did not need to convince them to come to Manchester United," he said. "This is the best team in the world. Everyone wants to be part of this squad. They are having a dream. I know how they feel. I found it very difficult when I first came here but I am here to help."