Drogba is still suffering from the concussion he suffered in the 3-1 victory over Norwich 11 days ago and Villas-Boas claimed the club would “push it to the limit” to ensure he was available for the trip to Old Trafford on Sunday week.

“He has to be authorised medically to make his full return to training,” Villas-Boas said.

“He has been doing light sessions, of course, with our physios.

“Let’s push it to the limit to try for him to be available for Man United.

“I wouldn’t say he would be available for Leverkusen.”

Villas-Boas added: “The first days were, of course, tremendous pain, and he had his family supporting him.

“He had complete support from the medical staff, who were with him 24-seven.

“And we’ve been getting this support to him.

“We just have to make sure that he’s fully recovered before he comes back to training because that’s the requirement you have to do neurologically.”

There was good news, otherwise, on the injury front for Villas-Boas, who confirmed goalkeeper Petr Cech was available against Sunderland after making a quicker-than-expected recovery from his knee injury.

Defender David Luiz is also back after missing the start of the season with a thigh problem.