He becomes City’s third signing of the transfer window after winger David Bentley joined on loan from Tottenham and central defender Curtis Davies arrived from Aston Villa in a £3.5m deal.

City’s acting chairman, Peter Pannu, told the club’s official website: “We are thrilled to have secured the three players in this window.

“It represents a comprehensive strengthening and support for our back four in Curtis, rejuvenation of the midfield in Bentley and further strengthening of the attack line in Martins.

“I am certain these new additions will augment and supplement what we already have and create some competition within the team for places which benefits the whole squad.”

Pannu is also hopeful that winger Sebastian Larsson will sign a new contract after failing to agree personal terms with Newcastle and Villa.

Larsson is out of contract in the summer and previous attempts to reach agreement over a new deal at St Andrew’s have faltered.

Pannu said: “Regarding Seb, although his agent had failed to reach any agreement with Newcastle and Villa , their loss may be our gain.