Gareth Southgate has moved quickly to reassure Middlesbrough fans that the club's record signing Afonso Alves will not be sidelined by a threatened legal challenge from AZ Alkmaar.The Dutch club claim they have a pre-contract agreement with the prolific Brazilian striker, who signed a four-and-a-half year contract with Boro last night following a month long-transfer wrangle. Alkmaar have announced they will take their case to FIFA, despite the Dutch FA having already ruled that the agreement between the player and AZ is invalid because the club failed to meet certain conditions. Speaking to Dutch newspaper De Telegraaf, chairman Dirk Scheringa said: 'He really has a chance of getting banned from playing for the rest of the season. We have a water-tight contract with him.' Alves disputes the claim and his new boss Southgate, when asked about Scheringa's threat, said: 'Well, that can't happen. The only thing that can happen is there could be compensation between Heerenveen and Alkmaar. 'The player has got international clearance and is registered to the Premier League so there's no way that can happen.' Of more immediate concern to Southgate is Alves' availability for Sunday's Tyne-Tees Premier League derby against Newcastle at St James' Park. The Boro boss did not sound too hopeful of unveiling the 27-year-old this weekend with the player having to spend most of today queuing for a UK visa at the British Embassy in Amsterdam. He said: 'It's looking like Sunday's game will come too soon for Afonso. We're now just waiting for him to get a visa so he can get back into the country. 'He's got international clearance, he's registered, he's our player and it's purely now about the fact that anybody coming to work in this country needs a working visa. 'We don't think he'll have that before the match but he'll certainly have it by the early part of next week. But this isn't just about one game, he's here for the long haul and there's plenty of time for him to make an impact. 'He hasn't played much football this year, so we don't want to rush things.'' Boro smashed their long-standing transfer record to sign Alves for a reported £12million. The club's previous record buy had been £8.15million Italian misfit Massimo Maccarone in June 2002, who came with a huge reputation but left on a free transfer early last year. Unlike Maccarone -- who had not played top-flight football when he left Italy -- Alves arrives with a prolific strike rate of 45 goals in 38 games for Dutch Eredivisie side Heerenveen and eight Brazil caps to his name. On finalising the deal, Southgate said: 'It's fantastic news. I went down to London with Keith Lamb on Thursday for the work permit hearing and, to be honest, I never thought it was going to be a problem because of the quality of the player. He's the Dutch player of the year and he was the top scorer over there last season. 'When you think there are players of the calibre of Klaas-Jan Huntelaar in the Dutch league and Afonso was out-scoring him, that shows you the measure of his achievements. 'We are delighted to have brought such a player here. He was very keen to come here, he wants to play in the Premier League and he wants to score goals for Boro.' Southgate could have done with having Alves available for the derby. Striker Tuncay Sanli faces up to four weeks on the sidelines after tearing a hamstring in the 1-0 midweek win over Wigan while Mido, who had a second run out from the bench inside four days on Tuesday, is clearly carrying a few extra pounds after his long lay-off due to a pelvic injury. Jeremie Aliadiere is expected to shake off a groin strain and start, while Stewart Downing, who took a nasty knock to the knee during Tuesday's game, is also likely to play.