Atletico Madrid are reportedly set to insert a €350m release clause into Joao Felix's contract, according to Diario AS.
The Benfica teenager is widely expected to complete his €120m move from Benfica when Antoine Griezmann completes his own €120m move to La Liga rivals FC Barcelona on July 1.
Diego Simeone's side look to have beaten off competition from arch rivals Real Madrid, and Pep Guardiola's Manchester City, to bring the Portuguese international to the Wanda Metropolitano.
Benfica are likely to insist on a sell-on clause in Felix's Atleti contract, as he is expected to continue his meteoric rise under Simeone, and in turn Los Rojiblancos will insert their own €350 release clause in the deal to safeguard their own interests.
If they are able to include the release clause into his contract, it will be the highest one implemented by the club in their history, surpassing the current record of €200m held by Griezmann.