"It was pretty hard when it happened. I just thought that I had twisted my knee and that I would only be out for a couple of weeks. Then when I went home and got the scan I realised it would be for a bit longer," he revealed.
Speaking as the Irish squad began their week-long training camp in Limerick, Ferris had to have surgery on his knee and was sidelined for six weeks but his recovery, aided by a stint in the ice chambers in Spala, has gone well.
"The main concern with my recovery was being ready in time for this week. I'm here now and have to put my hand up (again) for inclusion in the World Cup squad.
"The last six months have been the trial. It's not going to all depend on these next two weeks in terms of who is going to get selected for the World Cup. But I'll put the hard work in this week as I have in any other week and give myself every opportunity of being there," added the County Armagh-born youngster.
Reflecting back on the summer tour to Argentina, Ferris admitted: "I was pleased I got playing in Argentina, even if was for only 42 minutes. It wasn't what I had hoped for but that's rugby. I just had to bounce back and get myself in good shape. I have been running since last week.
"I feel I'm coming along well and just have to keep progressing. Argentina was a good opportunity. Even though I only got 40-plus minutes, I put my hand up and just hope that's what Eddie (O'Sullivan) was looking for (on the tour)."
Ireland coach O'Sullivan will announce his 30-man World Cup squad on August 12, a day after the warm-up match against Scotland at Murrayfield.
In his own words it would mean "everything" for Ferris, who is a current member of the IRFU/PricewaterhouseCoopers High Performance Select Group, to be one of the 30 selected players. "I know I have only been playing rugby professionally for a couple of seasons but if you asked anyone do you want to play for your country at the highest level, there would be only one answer. It would be unbelievable."