Jose Mourinho has said that the injury forced him off the Champions League match on Tuesady against Real Betis.
"This situation is not easy and the boy is playing sometimes not feeling 100 per cent," said Mourinho.
"The reality is he is not playing well or feeling confident and this bad feeling in the hamstring coming from the spine is not good," Mourinho said.
"It's quite a strange situation, not a typical muscular injury.
"We feel it's not an injury that can become worse if he plays so sometimes we say 'okay let's go and try'."
Although Chelsea's doctors have diagnosed the problem, even Mourinho admits that "solving it is quite difficult as there is no miracle".
And the Portuguese stressed reports indicating the pair had fallen out after the 65th-minute substitution against Betis were wide of the mark.
"I understand what it looks like but he was injured again," he added.
"I would say to you if he was disappointed because I changed him, but he was disappointed because he was injured.
"He was making a sign from the pitch saying he couldn't carry on. He was running a little bit out of control and disappointed because of the injury."