Emi Martínez has been taken to hospital after he suffered a head injury during Chelsea's Premier League match against Everton on Saturday.
Chelsea coach Xabi Alonso told reporters that the Argentina international was conscious when leaving the stadium and has been taken to hospital for "precautionary tests," adding: "For now, we need to wait."
He added: "It was a concussion, but more than that. I saw just one clip, but we'll have to wait."
Martínez, 34, collided with Everton's Jarrad Branthwaite when rushing from his goal to attempt to punch an Everton free kick out of his penalty area in the 67th minute of Saturday's match at the Hill Dickinson Stadium.
Both players received treatment on the pitch, with the Everton defender recovering quickly. Martínez, however, received extended treatment from the Chelsea physios and paramedics before being stretchered from the field while receiving oxygen.
He was replaced by 21-year-old substitute goalkeeper Mike Penders in the 75th minute. Eleven minutes of injury time were added on by the officials at the end of the match following the lengthy stoppage in play.
Two goals from Pedro Neto ensured Chelsea took all three points from their trip to Merseyside.
"We are really pleased. Shame for Emi, but we wish you all the best. This win is for him," Neto told TNT Sports.
Everton manager David Moyes said: "I just said to TV, I've not seen the Martínez injury yet, so I hope he's fine. I really do. I couldn't even see from the dugout. It just looked as if it was a sharing ball in between a couple of people. I don't know what else happened."
Chelsea's victory put an end to Everton's unbeaten start to the campaign and saw their defense hold firm for the first time this season.
"I'm really pleased with the performance, with the win, with the clean sheet," Alonso said. "There are many positives to build on from today. We knew it was going to be a hard challenge to win in this stadium, but we did many things to deserve the win. I think we got many things right. We were very professional, very solid, and it's good to have this feeling to win this way.
"We needed to feel like we could win in this way -- being solid, being strong, looking in control and going through difficult moments.
"In the first half, there were moments where there were corners and throw-ins and you need to overcome these moments. It's very hard in the Premier League to have full control of the game but you need to make sure you don't lose your shape or your condition, and today we did that really well."
Information from ESPN's Beth Lindop contributed to this story.