Michael Ballack
Ballack played under Jose Mourinho during his first spell at Chelsea. REUTERS

Michael Ballack has questioned Jose Mourinho's tactics at Chelsea and has claimed that Juan Mata's continued absence from the starting line-up is a mistake.

The Spanish maestro has started just 11 Premier League games this season and is yet to score a goal despite being a key player during the last two campaigns, winning the Player of the Season award two years in a row and leading the Blues to successive Champions League and Europa League triumphs.

Asking about Mata's exile from the Mourinho's line-up, Ballack, who played under the Portuguese coach during his first spell at West London, was quoted as saying in A Bola: "I can't understand why Mourinho is having trouble to get his best from his forwards and I think not playing Mata is a mistake."

Mata has been left on the bench in crucial games against Manchester United (twice) City, Arsenal and Liverpool during this season and has been an unused substitute in the club's last three games.

With the summer's World Cup on the horizon Mata's immediate future appears increasingly uncertain at Stamford Bridge after recent reports claimed that Manchester United are considering move to sign the Chelsea midfielder in January for a reported fee of £37m.

Furthermore, Ballack, who won a Premier League title and three FA Cups during his spell at Chelsea but lost the 2008 Champions League Final against Manchester United, spoke about the Blues' chances in Europe's biggest competition in their last 16 clash against Galatasaray:

"Galatasaray are a major club in European football and it won't be an easy game for Chelsea – but I expect them to qualify," Ballack added.

"Over two legs anything can happen, Didier Drogba is still a great striker and his experience as well as his leadership qualities really count in games like these."