Aitor Karanka says it's difficult to understand how Cristhian Stuani has been called up for international duty after the striker was summoned by Uruguay this week.
Stuani has been sidelined with injury since returning from the last international break and has not kicked a ball for Boro since September.
Despite Boro having presented the Uruguayan FA with Stuani's medical update, the striker's home nation have deemed him fit to play in the upcoming World Cup qualifiers against Ecuador and Chile.
"It's difficult for me to understand because I think the national team is a result of the work you do for your club," said Karanka.
"So for this reason it's difficult to understand how a player who has been injured for over a month is in the team.
"I didn't want to take a risk with him. The players who are not training with me are not in my mind to take a position in the team so I don't understand a team who selects a player that hasn't been playing.
"But it's not my concern. My concern is the players who are here, the players who were playing last month and those who are going to play in the next game."
"I can't do anything as a coach and the club can't do anything. So we're lucky because the next international break is in March so we have three or four months.
"But again, I prefer to speak about the players who are here."