Captain Johnny Sexton has been sidelined since leading Ireland to March's Six Nations Grand Slam and aged 37 the experienced playmaker is unlikely to feature again for the province.
His next appearances will be in the green of his country, in the build-up to the Rugby World Cup, starting in September. After that competition, he is expected to retire.
In a glittering career, Sexton has won the Six Nations and the Champions Cup four times and in 2018 was named World Rugby player of the year.
"He's one of the most influential players ever in Irish rugby," former Ireland hooker Bernard Jackman told AFP on Monday.
"Leinster will definitely miss him.
"I know he was gutted when he got that injury because all season his goal was Grand Slam with Ireland, Champions Cup with Leinster, and a World Cup with Ireland," Jackman added.
At Lansdowne Road this weekend, long-standing second-choice Ross Byrne is set to deputise for Sexton. The 28-year-old is just one of the pretenders to take over in the Test and provincial number 10 shirt in the long-term.
"I actually coached him at school," Jackman said of Byrne.
"We had a good team at St Michael's, we struggled against a small school in the first round of the cup.
"And in the 14th minute of injury time, he kicked a penalty from 40m to level the game. Then in the replay, we won and we won the cup that year.
"He's always had, in Ireland we say, big balls, this mental strength where he enjoyed pressure," the former Leinster front-rower added.
'Fascinating'
Among those competing with Byrne for the Ireland outside-half position will be his younger brother and Leinster team-mate Harry and Munster's Joey Carbery and Jack Crowley.
Crowley, 23, kicked a late drop goal last weekend as Munster stunned Leinster to reach this month's United Rugby Championship.
"He can play centre, he's a very good 10 and had his big moment on Saturday," Jackman said.
"Andy Farrell really likes him.
"He's more of a running threat than Ross Byrne, younger, less experienced too, but the battle between Ross Byrne and Jack Crowley will be fascinating for Leinster and Munster and Ireland," Jackman added.
Coaching La Rochelle this weekend will be former Ireland fly-half Ronan O'Gara, who Sexton took over from.
O'Gara played 130 Tests, winning a Six Nations Grand Slam and two Champions Cups for Munster.
"I don't think the next 10 is going to be as dominant as Ronan O'Gara or Johnny Sexton were in terms of being number one for eight, nine years," Jackman said.
"It's going to be really interesting," he added.
During his absence over the recent weeks, Sexton has been seen in the stadium, watching games attentively. On Saturday he is unlikely to change the habit.
"I think off the field this week he'll still have a big role," Jackman said.
"He'll try and help Harry and Ross Byrne. He'll look at where Leinster will attack La Rochelle.
"Not having him on the field is a big boost for La Rochelle," he added.
