MIDDLESBROUGH last night made Chelsea midfielder Nathaniel Chalobah their second January signing, with Aitor Karanka adamant that any player coming in does not destabilise a winning team.

Chalobah ended his spell at Nottingham Forest on Wednesday and the England under-21 international has made Middlesbrough his next destination, signing on loan until the end of the season - the second Chelsea player to sign this January following the acquisition of Kenneth Omeruo last week.

The 19-year-old is no stranger to the Championship with 12 appearances for Forest under his belt this season, having played for Watford last year. He is a player who Boro have courted since that spell, with previous manager Tony Mowbray coming close to signing him over the summer.

The deal has been concluded in time for him to be available to face Charlton Athletic at the Riverside Stadium tomorrow, but there will be no guarantees that he will feature, with Aitor Karanka reluctant to reshuffle his squad at the last minute.

Defender Omeruo, for instance, was not in the matchday squad for the 2-0 win at Blackpool, and Karanka does not want to disrupt his team by bringing new players in too soon.

“The most important thing is the players that are playing at the moment, they are playing very well,” said Karanka of Omeruo, who is returning from injury. “Ken is improving, and he needs to keep working. He knows how difficult it is to play in this league, there are many games to come and he needs to be ready.”

The Northern Echo: NEW BOY: Kenneth Omeruo has targeted a challenge to the Championship's top six while at Middlesbrough

Karanka has kept his counsel with regard to transfer prospects, but conceded that any players that do come in do not harm the team spirit he has helped to foster since taking charge in October, while also mindful that he would like to reduce the overall size of the squad.

“We are looking to sign more players but the most important thing is to keep the squad to 23-24 players,” said Karanka. “We need to keep the squad down. But it is good at the moment as the players are all doing well.

“Always in these moments there are rumours. They can be possible, they can’t be possible. We’re working to strengthen the squad.

“There are positions we’re looking at. With Ken, we have one defender, maybe one midfielder to come, there is no position we need more than the others.

“All the players who are playing now are playing well, and I don’t want to sign one player to break the philosophy and the mentality we have. For this we need to be very sure.”

Karanka is learning about his squad every day, but has seemingly made his mind up on Matty Dolan, who returned from his loan spell at Hartlepool United last week.

It was understood that Dolan would feature in Boro’s development squad against Arsenal on Wednesday, but the midfielder was not involved.

The Northern Echo: DOING WELL: Matty Dolan

Instead, Dolan, who is out of contract in the summer, is expected to go out on loan again, with Pools and Bradford City heading the queue for his services.

Karanka explained: “We are working with Matty to go on loan. He’s a good player but he’s a player I don’t know at this moment.

“He’s training with us sometimes but it’s better if he played, if he goes on loan. We have a lot of players in the squad at the moment and I think it’s better for him to play rather than train.

“I’ve been here two months, and my knowledge of the squad was not perfect at the beginning. I had players that hadn’t played and that I didn’t know, but I do now, and we are working on strengthening in certain positions.”