Frank Lampard admits Christian Pulisic remains a 'work in progress' as his hamstrings continue to cause concern heading into Chelsea's hectic Christmas run.
The US international had already missed 10 matches this season before he was left on the bench for Tuesday's Champions League draw with Krasnodar.
Pulisic also suffered an injury-ridden first year in English football but, when fit, has proven himself to be one of Chelsea's most potent attacking weapons.
Earlier this season he was dogged by complications surrounding a hamstring problem – first sustained in the FA Cup final back in August.