The French side battled back from 16-7 down to win 17-16 against the Aviva Premiership leaders, putting themselves top of Pool 3 by four points.
However, McCall has refused to concede defeat and is looking to December's double header with Italian outfit Zebre to get their challenge back on track.
"It's unbelievably disappointing to lose," he told Sky Sports News. "This result puts Toulouse in control of the group to a degree, but we still have a lot to play for.
"We must do the job when we have Zebre back to back in December. It was a really tight game.
"Toulouse are a very good team and we had to fight really hard in defence. For an hour we controlled them pretty well."
Sarries travel to Northampton in the Premiership next Saturday.