Middlesbrough head coach Aitor Karanka has criticised his side and threatened to drop players because they are not implementing his tactical plan.
Five wins in six Championship matches lifted Boro to ninth on 18 January.
But two points from their next three games, during which they have failed to score, has seen them fall to 13th.
"It's not the side I saw [on Boxing Day]. We must press teams. I'll change the players if we do not recover that style," he told BBC Tees.
There was significant activity on Teesside during the January transfer window, particularly in terms out outgoings.
Ten players left the club, while Kenneth Omeruo, Nathaniel Chalobah, Lee Tomlin and Danny Graham came in, and Daniel Ayala made his loan stay permanent.
Eight of those departures were on temporary deals, taking the number of Middlesbrough players out on loan to 11.
"Maybe the players were distracted by the transfer window. It's like they've forgotten what I want them to do," added Karanka.
"Hopefully, now it is closed, the squad can be more focused and start using our pressing style of play again.
"They need to because I am not happy. I don't understand because we're one month ago, not two years ago, they were doing the right things."