Ashton had an impressive debut, contributing two tries to Saracens' 40-3 win at Twickenham.
"He brings something different, he's never far away from where the action is, particularly when we've got the ball," said McCall after the match.
"He pops up in unusual positions, which is exactly what we wanted. We are hoping he will take our attacking game forward.
"He played really well today and a lot of the others did too."
Ashton also received a yellow card in the first half for blocking a potential London Irish attack.