Sarries overturned an 11-3 half-time deficit to claim a ninth Premiership away success in a row yet McCall is expecting more from his men when they begin their European campaign at home to Benetton Treviso and then away at Biarritz Olympique.
"Overall, we're going to have to do a lot better," said McCall, after a 75th-minute converted score from Brad Barritt stole the show in the West Country.
"We were disappointed with a lot of aspects of our performance. We did a lot of things poorly. Our discipline was poor and we got rattled from time to time.
"We've got a 13-game run now with big European games just around the corner and, although it's great to have won another away game, we talk about performance all the time and this wasn't our best.
"Treviso won by 50 points against the Dragons in the RaboDirect PRO12 at the weekend. They've won four in a row so they're going to be a very difficult proposition."
McCall, whose men also face former Celtic Kings the Ospreys in Pool 5 of the Heineken Cup, couldn't fault his side's resolve, however, as they came back from 17-9 down to make it six league wins from seven this term.
Sarries showed great togetherness and team spirit to grind out a victory that looked beyond them for much of the match and they did so in front of arguably the most vociferous crowd in English Rugby.
They now head towards their continental campaign full of confidence and undaunted by the prospect to trips to the Stade Aguilera, Liberty Stadium and the Stadio di Monigo.
"This group is pretty special and they found a way to win," added McCall, whose team lost five times in the group stages last season.
"Although it wasn't our best performance and probably wasn't a great match to watch, it was a magnificent win. As a collective, we stayed tight and that was why we got the result.
"I can understand why a lot of teams come down to Kingsholm and get beaten heavily because of the crowd and the intensity that Gloucester bring to the game. The fact that we were able to stay tight, not completely lose ourselves and show the composure required in the last quarter says a lot about the group.
"The players enjoy going to places like Kingsholm, to Franklin's Gardens and to Welford Road. As soon as you start over-analyzing being away from home you've made a massive mistake. We don't talk about whether we're home or away: we just have good players, with a great attitude who get stuck into their preparation every week.
"It doesn't really matter whether it's Vicarage Road or somewhere else, they give their best and they get stuck in."