Costa has refused to commit to the club and was frustrated a January move fell through.
"Basically, a decision on which player we are going to buy in the summer has been made. And we have secured a verbal agreement with the player as well as his club," Tianjin Quanjian owner Shu Yuhui confirmed.
"We have not signed a formal contract yet, and I will not reveal the player's name during the sensitive period.
"Buying a world-class centre forward is a no-brainer."