James Ryan says Leinster's Champions Cup disappointment reinforces the need to seize the moment when it presents itself. Ryan was made up to receive his British & Irish Lions call-up after missing the South Africa tour four years ago because of injury The Leinster and Ireland second row knows that his Leinster colleagues Sam Prendergast and Robbie Henshaw were disappointed to miss out but he is backing them to show they can do a job if called up late. Caelan Doris, however, doesn't have that chance and Ryan understands the pain the Leinster and Ireland skipper is feeling to miss out after shoulder surgery. "It was nervy, there were a lot of distractions, reviewing Northampton and then at the back of our mind was the Lions," he said. "It’s always in the back of your mind and it’s great that so many of us were able to go. It's hugely disappointing for Caelan and the lads are gutted for him. "At least some of us have some more rugby to play after such a disappointing couple of weeks, but for him to be out after that game for the next four to six months is heart-breaking. "He’s someone that is genuinely hard-working and invests a lot of time off the pitch in terms of getting better, a professional in every sense. So for him to be missing the rest of the season for Leinster and then obviously the summer is tough for him." Ryan made his comeback in the record URC rout of Zebre last Saturday from a calf injury that sidelined him for two months. It was hard for him to watch the Champions Cup semi-final loss to Northampton and he described the review that followed as "open and honest", adding: "We put our hands up, we weren’t good enough, it was very disappointing. "Our focus was on responding and bouncing back and we did that well. We need to back it up with performances against Glasgow and then in a quarter-final at the Aviva. We have to keep up that standard in the next few weeks. "When it comes to knockout rugby, you need to be at your very best and we weren’t against Northampton and there were many reasons for that. We need to be at our very best for the knock-outs." Leinster travel to Scotstoun on Saturday to face the reigning champions who were on course for second spot behind the province and a home path through to the semi-finals. But after back to back defeats to the Bulls and Benetton, Glasgow have fallen to third place. "They’re coming in off a couple of losses and they will be fired up," said Ryan. "Sione Tuipultou coming back in is a big boost and maybe they dropped in the league so they have a lot to play for. "They want a home quarter-final and not have to go to South Africa. They’ll be disappointed with how they performed in the Champions Cup. I’m sure you'll get a different Glasgow. "We want to win silverware, so does everyone else. It’s exciting to have a home quarter-final and we want a performance for our supporters to be proud of. "A week is a long time in sport. The older I get the more I get what that means. It was tough watching on in the last number of weeks. You have to soak it up and enjoy what you can - and hopefully we have a good few weeks to look forward to." Get the latest sports headlines straight to your inbox by signing up for free email alerts.