Didier Drogba was taken to hospital with mild concussion after being knocked unconscious during Chelsea's 3-1 victory over Norwich in the Premier League on Saturday.

The injury overshadowed Chelsea's second victory of the season, which was wrapped up by Juan Mata scoring on his debut in the 11th minute of stoppage time resulting from Drogba's injury.

The Ivory Coast striker's head was caught in a collision with Norwich goalkeeper John Ruddy and he was carried off on a stretcher wearing what appeared to be a breathing aid following seven minutes' treatment on the pitch.

''Drogba will be released from hospital tonight following medical tests,'' Chelsea said on its website. ''The club's medical staff will continue to monitor the 33-year-old over the coming days.''

Drogba remained unconscious ''for quite some time'' after leaving the Stamford Bridge pitch, manager Andre Villas-Boas said after the match.

''We are just waiting for the full exams on his concussion and hopefully nothing is wrong,'' Villas-Boas said. ''He is showing some good signs of recovery for us to be a little bit more tranquil.''

Villas-Boas said the challenge ''looked pretty nasty.''

''He lost consciousness completely on the pitch,'' the manager said. ''I have to be very, very grateful, not only to my players but to the Norwich players and to my medical staff for reacting so quickly to a potentially dangerous situation.''

The injury came just after Grant Holt pounced on a mistake by Chelsea goalkeeper Hilario in the 63rd minute to equalize for Norwich.

Hilario needlessly came racing off his line to claim a cross and collided with Branislav Ivanovic, allowing Holt to hook the ball into the empty net.

Jose Bosingwa had put Chelsea ahead after just six minutes with his first goal since November 2008 coming from a 25-yard (meter) strike that went in off the inside of the post.

Frank Lampard restored Chelsea's lead from the penalty spot in the 82nd after Ruddy was sent off for fouling Ramires.

It sparked a flash point between the benches, with Norwich manager Paul Lambert shoving Chelsea coach Jose Mario Rocha after the latter entered the visitors' technical area to celebrate the spotkick.

Lambert described Rocha as ''the guy with the stopwatch on his neck'', adding: ''I don't know who he is but he's flown right into our area.

''I'm not fluent in Portuguese so if he understands Glaswegian then he might know what I said. You don't do that - it's disrespectful.''

Chelsea manager Andre Villas-Boas backed Rocha.

''It's difficult to control your own emotions on the bench,'' he said. ''But I would find it very, very strange if my technical staff would be disrespectful of Norwich and maybe they were just showing some emotions. If Paul can't handle that, I'm sorry - unlucky.''

It was a dream debut for Mata, who came off the bench and produced Chelsea's third goal three days after joining from Valencia.

Ritchie De Laet presented the Spain midfielder with the ball and he slotted beyond replacement 'keeper Declan Rudd.

''I'm very, very happy that the team is able to control their state of mind, to fight back, to show commitment and desire,'' Villas-Boas said.