The 25-year-old received the punishment following a disciplinary hearing over a dangerous tackle on Northampton’s Vasily Artemyev in a 16-6 victory at Franklin’s Garden.
It was Ashton’s third yellow card for foul play this season and England head coach Lancaster is hoping to address the issue.
“He needs to improve his style of tackle because clearly it’s been an issue,” said Lancaster.
“It’s something we’ve spoken to him about, in terms of his tackle technique but also making sure he controls his competitive nature.”
“We’ll work on it this week because he’s in camp with us.
“It’s not something which can’t be solved pretty quickly and hopefully it won’t be a repeat occurrence.”
Meanwhile, the England head coach hinted that Freddie Burns will not be making his debut this weekend after the Gloucester fly-half was called up to the squad as cover.
“For a fly-half to come into any team and take control of it without really knowing the structures and systems you’re playing with, it’s very difficult,” added Lancaster.
“Also, I do think Toby Flood has played extremely well recently and Owen Farrell the same. So it’s great that we’ve got that quality in that key position.”
MORE: The latest football news
MORE: The latest tennis news
BIOGRAPHY: Jerome Boateng
BIOGRAPHY: Danny Rose