Farrell will be seconded from his role as Saracens head coach to work alongside Stuart Lancaster and Graham Rowntree in England's interim coaching set-up.
The former dual international, who is less than two years into his coaching career, was initially reluctant to take up the opportunity until Saracens urged him to do it.
"As a club we are massively keen to develop individuals," director of rugby McCall said after Saracens' 31-26 Heineken Cup win over Ospreys.
"Although the team is important, developing individuals is what we are about, whether they are coaches or players.
"When you get a chance to coach the Six Nations, it would be unfair to say no.
"As a coach he is outstanding. We will miss him when he is away because he is a big part of what we do, but he will be back here coaching this club for a very long time.
"He is a born winner and I am glad he has the opportunity to coach at that level."
One of the biggest questions Farrell will have to answer is whether to select his son, Owen, who kicked 16 points at Wembley tonight.
Farrell junior's second-half sin-binning could have cost his side and did affect a change in momentum that allowed Ospreys to earn a losing bonus point.
But Farrell had done enough by then to set Saracens on course for a victory that carries them to the top of Pool Five.
"Owen had a great match," McCall said. "He is key for us whether he plays 10 or plays centre."
Farrell started at outside centre and moved to fly-half when Charlie Hodgson went off, while Alex Goode also caught the eye at full-back.
"There were a lot of good performances from our English guys today," McCall added.
Rhys Gill, Ernst Joubert and Chris Wyles scored the tries for Saracens who were in full control until Farrell's sin-binning for a body-check on Dan Biggar took the wind out of their sails.
The Ospreys took advantage with centre Ashley Beck scoring his second try of the match.
Saracens held on for the victory but Biggar's 16-point haul ensured the Ospreys left London with a bonus point, which could be valuable in such a tight group.
The Welsh region's director of coaching Scott Johnson described it as the "best worst result we could have asked for".
Johnson was furious with the way the scrum was refereed and he believes the rugby authorities must act as a matter of urgency to preserve its place in the game.
"The scrum has become a lottery. It is getting to the point of being farcical," Johnson said.
"I may not be a scrum guru but I can tell you the illegalities were not all one way.
"We are playing off two scrums a game - one each. It is just short-arm free-kick, penalty. You may as well toss a coin and say 'whose go this time?'
"That is the stage we have got to in this game of rugby. We have got to do something about the scrums because they have become farcical.
"Clearly it is not working, when you don't get the foundation. The back lines were moved back five metres (in a law change) to try and get them space to play rugby.
"We have to look at the issue here. The mandate is clear, it is a game for all shapes and sizes. It is the same for both sides. You can get a free kick or a penalty and not know what to do.
"You could have ascendancy in the scrum but it is an absolute lottery."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.