Borthwick was making his 100th cap for the club while Fraser, who has enjoyed an extended run in the first team recently, was named Sky's man-of-the-match.
"Steve is absolutely vital to us," McCall said.
"He's actually playing really well, he's had a really good couple of seasons not just this season but last season too. He led from the front.
"Steve plays a lot and we certainly have to look after him so that he's fresh at the end of the season. He had a couple of weeks off for the LV Cup and we'll continue to look after him.
"I thought Will Fraser - who was named Sky's man of the man of the match was up there too. Will kind of epitomised our physical effort out there."
McCall also singled out Charlie Hodgson who kicked 23 points in the victory.
He said: "Charlie's had a wonderful season for us and I thought in the second half he just got us in the right areas but he also kicked his goals at the vital times."
Saracens now face two crunch ties against Munster in the Heineken Cup, the first of which takes place at Thomond Park on Saturday.
And McCall insisted the returning international players would be involved in those games but admitted some would have to be rested afterwards.
"We've got Munster back to back so everyone will be in next week," he continued.
"We took the decision to give Kelly Brown and Schalke Brits the week off to freshen up - we take a long-term view on all the players.
"Although the English internationals will come back in and be involved in the Munster games, they will be rested after those games - it's important that we look after them."