The 23-year-old second rower enjoyed the proudest moment of his career when he made his Test debut in last Saturday's 34-12 win over Fiji in Hull but says that will be at least matched if he keeps his spot for Saturday night's last-eight clash with France at the DW Stadium.
Farrell was in England's 19-man squad for each of the first two games of the World Cup but was one of those omitted when McNamara finalised his line-up.
"It was quite tough," he admitted. "When he said to me I wasn't playing against Australia, I found it quite hard but, after a day or so, I was behind the lads completely.
"Then he hinted to me a couple of times earlier in the week that I would be playing against Fiji but it never really clicked.
"I was over the moon to get my chance. I only got 25 minutes but I was still playing for my country and hopefully I might get another shot this weekend.
"It would be the ultimate, to do that in front of a lot of Wiganers. It would be up there with making my debut."
There could be as many as six Wigan players involved when McNamara announces his 19-man squad on Thursday afternoon, with prop Lee Mossop and winger Josh Charnley hoping for recalls .
Charnley, who scored his 44th try of the year in England's opening match against Australia, is hoping to get the nod after losing out to Tom Briscoe for the last two games.
"Everyone wants to play so we are all fighting for spots and, if anything, it helps us play better as individuals," Charnley said.
"I have got to train hard this week to get the nod because Tom Briscoe and Ryan Hall have been good. There is a lot of competition in the squad, but if I do get to start it will be exciting to play at Wigan for the last time this year."
England are firm favourites to secure a place in the Wembley semi-finals but Farrell says they will not underestimate the challenge of the French.
"When I look at France, I see a lot of Catalans and they're a tough, aggressive team," Farrell said.
"They use their forwards a lot. They are big but, if we match it with our forwards, I think we will give ourselves a good chance of winning.
"I think it will be similar to the way we played against Fiji. They were big and aggressive. I think we've got a forward pack to destroy most teams in the competition."
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