Strained or pulled knee ligaments are notorious for giving future problems.
My injury to my left knee , skiing 28 years ago, still occasionally gives me "Gip" , especially if I put too much pressure on it on the bike. I just rest it a bit, massage it with my fingers and get right back on the bike but I take it easy.Usually, in a day or so, it's back to as normal as I will ever have it. I did have arthroscopic surgery but all that did was suck out the torn ligament debris but it was very effective at reducing the inflammation and pain and within a week of that minor limping for 2 years.
Ligaments do not have their own blood supply so they get their nourishment from absorbing nutrients by a process of osmosis from surrounding tissue. And that is another reason why healing can be so slow.
But with all the assistance that he will have at the club no doubt he will be back again shortly.M aybe the minor surgery referred to was arthroscopic.