Real Valladolid have accused Manchester City of advising their defender Juma Bah to break his ­contract and not train on Tuesday to force a cheaper move to the Premier League champions, with the Spanish club threatening legal action.

Bah, an 18-year-old centre-back, joined Valladolid in August and became the first Sierra Leonean to play in La Liga. The club say Bah has bought out his youth ­contract after refusing to sign a senior deal that would have made him more expensive.

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City are thought to have been in discussions with Valladolid regarding a fee of about £6.75m. The cost to Bah of buying out his juvenil (under-19) terms was €6m (£5.1m), for which he would be reimbursed by City.

It is a legal requirement in Spain for every player’s contract to have a buyout clause and Bah’s would have been €30m had he signed a renewal on a senior contract or €12m on a B-team deal.

Valladolid said in a statement: “Abdulai Juma Bah and his agent yesterday afternoon informed Real Valladolid of their intention to unilaterally break their contract with the club. Before that, also yesterday afternoon, Manchester City sent a letter in which they requested that Real Valladolid open negotiations for the player with a view to a possible permanent transfer.

“Today, the Sierra Leonean decided not to show up at his place of work for the ­morning training session. For those ­reasons, the club considers the player ­responsible for not fulfilling his ­contractual obligations, and has requested the club’s legal department to begin disciplinary procedures.

“The club believes that Manchester City, part of the City Football Group, is behind the player’s decision, and appears to have advised the player to adopt this path, which puts Real Valladolid in a position of defencelessness, having previously rejected higher offers, and all the more so when the player is still at the juvenil phase and had recently refused to register for a [Valladolid] team of a higher category, given that to do so would have meant an automatic increase in his buyout clause.”

Valladolid said “all three ­parties” – an apparent reference to City, Bah and the agent – had been warned “of the possible ­consequences of their actions” and that the events had caused “great disappointment and indignation” at a club that had welcomed Bah “with open arms and gave him the opportunity of his life”.

Valladolid said the Spanish football federation had confirmed Bah had deposited the money to rescind his contract and that the club “reserves the right to take the opportune sporting and legal measures it sees fit in defence of its rights and its interests”.

The Guardian approached City for comment. Bah would be the third central defender to join this month, after Abdukodir Khusanov and Vitor Reis.

Kyle Walker is a target for Milan but City are yet to receive an official offer for the 34-year-old. Any deal to take the defender to the Italian club is expected to be a loan.