The 31-year-old's presence will guarantee a media sideshow, but although Newcastle have lost their own superstar Jonny Wilkinson to another knee injury, Fletcher is upbeat about his team's prospects.
"Coming from league to union, and having had such a long time out to injury, I would say perhaps they might give him (Farrell) a little bit of a run from the bench, if anything," said Fletcher.
"It is none of my business realy though, we are just concentrating on facing Saracens as a team.
"They have a lot of good players, and the press attention surrounding Farrell is not what we are thinking about."
The Newcastle forwards endured some testing times against opening Premiership opponents Northampton and Worcester, suggesting Saracens will go for the jugular in set-piece situations.
But Fletcher added: "Saracens may well target our scrum, yet we coped well in that area (against Worcester) last week and we are improving a lot there, so we would expect to get parity.
The way we are trying to play the game is very tough. We want to move the ball around and play from all areas of the pitch with plenty of pace.
"We have looked at that this week, and we know we have to play more of the game in the opposition half.
"A lot of the teams we've seen so far have played a very conservative game, and the stats bear it out.
"We made 153 passess against Worcester, with only five handling errors, while Worcester made something like 60 passes all game, and around 40 of those were from scrum-half.
"That says a lot about how we are aspiring to play compared to other sides, but we accept there needs to be a bit more of a balance and we are working on that."
Saracens have stumbled into the Premiership season through a defeat against Wasps and 13-13 draw against Bristol, yet Farrell could give them just the lift they require to record an opening win.
"We were delighted at the way Andy came through the game on Monday night and the impact he had on the match," said Saracens rugby director Alan Gaffney.
"He did a number of things very well despite it being his first action for a long time. He has trained very hard this week and, as a result, he deserves his place on the bench."
Gaffney, meanwhile, has made five changes from the Bristol game, calling up wings Kameli Ratuvou and Rodd Penney, together with forwards Matt Cairns, Kris Chesney and Ben Russell.
Like Saracens, Harlequins are seeking a first Premiership victory of the campaign, but it is unlikely to arrive against unbeaten Wasps at Adams Park on Sunday.
Quins have collected just a solitary losing bonus point from two games, and they will be without ex-Wasps centre Stuart Abbott because of suspension.
Wasps, buoyant after making their best start to a league campaign since 1997, welcome back England lock Simon Shaw following his recovery from a finger injury, with fly-half Jeremy Staunton named at inside centre as Dave Walder and Eoin Reddan forge the half-back partnership.