The sides are locked on 10 points each going into the Pool One encounter at Vicarage Road, with Munster winning last weekend's clash 15-9 in Limerick.
"I think we probably need to improve in all areas - we were well below our best last week," rugby director McCall said.
"We set ourselves high standards as a team, and in certain areas (last Saturday) we felt that those standards fell short. We can rectify those areas and I think we'll be better on Sunday.
"There was nothing wrong with our effort and our physicality. In the second half the team showed a lot of character and a whole lot of fight to ensure we came away with something from the match.
"Munster is a difficult place to go, and when you think they have only lost three matches in something like 50-odd (Heineken Cup) games down the years (at home) it was always going to be tough.
"Now that the international players are back in our system we've had a good training week and a longer training week than when we had a six-day turnaround after the Gloucester league games, so I think we are in a much better position for this game."
Steve Borthwick skippers a Saracens team that includes current England internationals Alex Goode, Chris Ashton, Brad Barritt and Owen Farrell, but Ireland centre Keith Earls misses out for Munster due to groin trouble, so Casey Laulala is recalled.
Sale Sharks enter the last-chance saloon in Pool Six when they head to Stade Felix Mayol for an appointment with one of the tournament favourites Toulon on Sunday.
Sale lost 17-6 against Toulon on home soil last Saturday, but the French club's remarkable squad strength is illustrated through the power of their replacements' bench on Sunday.
England internationals Jonny Wilkinson, Andrew Sheridan and Simon Shaw are among the substitutes, together with Argentina Test captain Juan Martin Fernandez Lobbe and former New Zealand prop Carl Hayman.
But the starting XV still contains players like Matt Giteau, Frederic Michalak, Gethin Jenkins, Bakkies Botha and Joe van Niekerk, which underlines Sale's acute degree of difficulty.
In Sunday's other game, Pool Four rivals Castres and Glasgow meet in France, where a victory for the home side would keep them in touch with group leaders Ulster. Glasgow, though, have collected just one point from three games.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The Barbarians are one of the top invitational rugby sides with a long history and classic rugby jersey.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Lions get ready for their matches with this green training jersey. It's what the players wear. Get in the Gear!
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 Lions are ready to get their Australia tour underway. They arrive in Perth on Monday.
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.