But Earls' quicker-than-expected recovery saw him back in the famous red jersey on Saturday to score an excellent try in the Lions' 26-24 win over the Cheetahs in Bloemfontein.
The Limerick youngster has been roundly praised for bouncing back from a shaky start to the tour playing-wise but also for his hard graft and determination in fighting off the injury and returning to full fitness.
Dr. James Robson, who is on his fifth Lions tour, said: "Keith had a collision-type of injury you see in a car accident, a seat belt-type of collision.
"He bled very badly into his pectoral muscle, and he strained his AC and SC joints.
"It's testament to his character and the hard work that both he and (our physio) Phil Pask, who has inflicted an awful lot of pain on the poor boy to get him back to excellent health, have done.
"Keith was having treatment about six times per day from first thing in the morning to last thing at night, so seeing him score the try was fantastic.
"The professionalism shown by the whole squad in their injury management is the best I have ever seen."
England centre Riki Flutey was another player who was facing an early flight home but a dedicated rehabilitation programme has enabled him to return to contact work today.
Flutey is available for selection for Wednesday's game against the Sharks in Durban, but Welsh flanker Martyn Williams will be given some extra time to recover from the shoulder injury he sustained against the Royals.
Robson added: "Riki did quite a nasty piece of damage to his knee a week ago, so much so that I thought he would be the first person out of South Africa.
"Almost two-hourly he has been attending treatment, and that includes treating himself through the night.
"He has been setting his own clock. His treatment included a pressure sleeve around the particular area, then you filter very cold water through it.
"It cools it down and puts it under intermittent pressure as well.
"It's all designed to help reduce swelling and promote blood supply to the deep tissues."