Manchester United are facing up to the prospect of beginning the new season without Carlos Tevez - and they may even have to wait beyond the transfer window to secure the striker.

FIFA have been called in to end the deadlock surrounding the Argentinian's move from West Ham.

Both clubs believe only the game's world governing body can end the impasse over the 23-year-old and have asked the Premier League to send the case to FIFA.

Manchester United remain confident he will eventually become their player but there remains a strong possibility Tevez, who has now been allowed to start a short holiday, might not be signed before the start of the season and the delay could even go beyond the August 31 transfer deadline.

United chief executive David Gill said: "Hopefully the case will be heard on an expedited basis but we are not sure whether we will have him signed in time for the new season.

"It may take up to two weeks for the body to be formed, all the paperwork has to be put together and then the case has to be heard.

"Even given that timetable we hope by the time the new season kicks off, Carlos will be training at Carrington."

Even if the dispute does drag on beyond the end of August, Tevez could still join United between transfer windows if FIFA declare him an effective free agent.

That scenario happened with Tevez's compatriot Javier Mascherano before he was finally allowed to link up with Liverpool earlier this year.

FIFA will be asked for their dispute resolution panel or players' status committee to step in and decide whether Tevez is fully bound by his existing contract with West Ham or not.

His deal still has three years to run and all the escape clauses and get-outs were contained in the third-party agreements with his adviser Kia Joorabchian, which were unilaterally terminated by the Hammers.

West Ham confirmed they have written to the Premier League this morning requesting the matter be referred to FIFA.

The letter from West Ham's lawyers states: "We write to request your written consent for this dispute to be heard by FIFA before their players' status committee or the dispute resolution chamber (whichever FIFA deems appropriate)."

A West Ham spokesman told PA Sport: "It now makes sense for this to be dealt with by FIFA.

"All parties agree this is the best way forward and of course we will be involved in helping this be resolved as quickly as possible."

United legal expert Maurice Watkins met with West Ham chairman Eggert Magnusson in London on Tuesday, but despite feeling reasonably optimistic a solution could be negotiated, instead there was only deadlock, and the Hammers blocked United's wish to give Tevez a medical this morning.

Earlier this week, Gill, an influential FA board member, suggested the whole saga had become "over-complicated".

However, it now looks like becoming even more problematic, with Sheffield United no doubt keenly interested in how the matter is eventually resolved given Tevez played such a huge role in sending them down.

"There have been a lot of discussions over the last few days between Manchester United, West Ham and the Premier League but the case will probably go before FIFA's dispute resolution chamber," added Gill, speaking in Seoul, Korea.

"We are very confident this will be resolved in favour of the player and he will be free to achieve his wish of joining Manchester United.

"All the discussions we have had over the last few weeks lead us to believe this will be resolved in Carlos's favour," said Gill.

"Once that happens, he will be free to join Manchester United."

While FIFA will examine all the documentation before deciding whether they have any jurisdiction over the case, it seems certain the Premier League - as well as West Ham - would be happy to abide by any decision.

So, instead of having his medical, Tevez will now go on holiday, hoping by the time he returns, he will only need to sign a contract to become a United player.

"It was always Sir Alex's plan to give Carlos a break, so I expect he will now go on an exotic holiday with his family," added Gill.

"He has not completed a medical with us."