Harlequins fly-half Demetri Catrakilis was taken to hospital after he stopped breathing for several seconds during his side's 28-17 Aviva Premiership victory over Gloucester.
South African-born Catrakilis was injured by a shoulder hitting him near his throat minutes after he had kicked the first penalty of the Twickenham Stoop contest.
Harlequins director of rugby John Kingston explained afterwards: "He has gone to hospital. He was struggling to breathe on the pitch. The area to breathe properly was not clearing which needed to get oxygen.
"We needed to get him to hospital. They will probably assess him overnight. It is precautionary but when you get a blockage like that, it is something you have to react quickly to.
"It was a shoulder to his throat. That was causing him difficulty and, indeed, he did not breathe for a few seconds. But then he started to and the oxygen helped him after he came off the pitch."
Catrakilis was replaced by 18-year-old Marcus Smith, who had an excellent game with two penalties and two conversions. Back-row Dave Ward and wings Charlie Walker and Marland Yarde also scored tries.
Kingston was pleased his team bounced back from the 39-29 defeat to London Irish at Twickenham last Saturday, saying: "The bottom line was I demanded a reaction from last week.
"That wasn't what we feel we are. With all due respect, the opposition played well. Today, we were working really hard for all the crumb sand the loose balls. Physicality was there and the work ethic.
"I have just said to them that if two games encompass what this league is about, it is there. You have to want it. If you are not absolutely desperate, you will come unstuck in this league."
Gloucester were never in front and only had a penalty from fly-half Billy Burns in the first period to show for their efforts.
They got back in the match after the break through a try by back-row Freddie Clarke, converted by Burns, before a late try from replacement Jacob Rowan, converted by Billy Twelvetrees.
The visitors were a shadow of the team which beat reigning champions Exeter on September 1 and new head coach Johan Ackermann said the performance was not acceptable.
The South African explained: "It was very disappointing, not the result but the way we played.
"I don't want to take anything away from Harlequins but the mistakes we made just made it easy for them.
"We must have a good look at ourselves. I knew we should not get over-excited about week one. This is a big disappointment but we will put it behind us."