By Jeremy Butler
MANCHESTER, England Aug 13 (Reuters) - Manchester United unveiled Argentina international signing Carlos Tevez on Monday and said they had an option to keep him longer than his original two-year deal.
Tevez joined the Premier League champions in a complicated deal from West Ham after playing a big part in saving the London club from relegation last season.
"We have a two-year deal and then we also have the right to purchase Carlos at any time within that period for a set sum," Manchester United chief executive David Gill told reporters.
"The fee is set down. We know what we have to do in terms of keeping him here for a longer period."
Gill refused to say how much United have initially paid or what they would have to pay to keep Tevez longer.
Tevez will make his debut at Portsmouth on Wednesday in place of Wayne Rooney, who will be out for the next two months because of a broken bone in his foot.
He believes he can build a partnership with Rooney on his return despite suggestions that the players are too similar in style. "Always the best players can play together," he told reporters. "I am only 50 percent similar to him."
West Ham and third party rights holder Kia Joorabchian had to agree on a deal to release Tevez before United could sign him.
DIFFICULT DEAL
"It was impossible not to know what was going on this summer," Tevez said. "I only really start to realise how difficult it was when I was playing in the Copa America. Each game passed and the situation wasn't being resolved.
"Obviously I am here now though and that is all that matters."
He added: "It was difficult for me to leave West Ham as well. In fact it hurt me to leave but the lure of Manchester United proved too much.
"It's a great step for me and now I need to write my own history at this club and do everything I can to make this club as successful as possible."
United manager Alex Ferguson said he has followed Tevez's career closely and watching him at West Ham last season convinced him to sign the forward.
"His profile with the national team is good," Ferguson said. "We watched him first when he was 18 years of age and we couldn't get work permits at that time.
"Then he was in the Olympic team at 20 and we watched him then and his progress through to international level.
"But without question his performances last year in the Premier League were the foundation we based our decision on."
Gill said he would like FIFA, the sport's international governing body, to making a ruling on whether third parties can own players in the future.

