Chelsea manager Andre Villas-Boas admits losing to Manchester City in their Monday night Premier League clash at Stamford Bridge would make winning the title "extremely difficult".
Defeat would leave the 2010 champions 13 points behind the leaders.
The 34-year-old Portuguese coach argues that midfielder Frank Lampard still has an important role to play at the club despite being substituted in last Saturday's win at Newcastle and not making it off the bench in their decisive midweek Champions League win over Valencia.
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