Jurgen Klopp is willing to raid his former club in a bid to solve the defensive crisis at Liverpool.

The Reds have no centre-backs available to play at the moment, after Dejan Lovren and Kolo Toure picked up injuries in the 1-0 win over Stoke City in the Capital One Cup semifinals. Martin Skrtel and Mamadou Sakho are already sidelined, while Joe Gomez, who can also play in the position, is a long-term absentee.

Liverpool have cut short Tiago Illori's loan at Aston Villa in a bid to have some kind of defence for the FA Cup match against Exeter. However, Klopp is now forced to go into the transfer market to try and sign a defender, with Borussia Dortmund man Neven Subotic his number one target.

Subotic enjoyed his best time as a player under Klopp and the German manager is hopeful of agreeing a loan move with Borussia Dortmund.

Liverpool are also looking at signing Andrea Ranocchia on a temporary deal from Inter Milan, according to the Daily Mirror, while Joel Matip is another option. Matip was initially being targeted for a free transfer in the summer when his contract expires with Schalke, but Klopp is now considering agreeing a deal with the Bundesliga club for the versatile player in January.

Meanwhile, Sunderland manager Sam Allardyce believes Liverpool's injury problems have stemmed from Klopp's high-pressing tactics combined with the unrelenting schedule of the festive season.

"That is him asking his players to play a high-tempo pressing game from the top end," Allardyce tild Talksport. "It's great that the players have been able to carry it out but I think it has kicked in now.

"I don't think Jurgen has realised just how ferocious our league is at this period of time and because he has asked for that extra high-energy, that extra ten yards, these lads are fatiguing now with so many games in much a short period of time and are picking up these muscle strains.

"They are highly-trained athletes more than ever before and they become more susceptible injuries by the amount of work they do in a game now."

Allardyce has been highly critical of the Premier League's schedule this season, with a full round of fixtures coming into play a few days after the FA Cup weekend.