The West Ham forward has suffered a number of setbacks since picking up an injury in September and he was forced to go under the knife again earlier this week.
The club have not put a timescale on his recovery but Ashton accepts that he is unlikely to be back before the end of the current campaign.
He insists the surgery was a success but does not want to take any risks and is looking ahead to next term.
"I think realistically pre-season is my target," Ashton told the Sunday Mirror.
"The surgeons are pleased but obviously it's a setback I didn't really want.
"I need to get over this operation, get myself properly fit and I don't want to rush back before I'm ready.
"It happened when I just thought I was back, especially after scoring twice in the first game - but then I came down with another complaint with my ankle."
Ashton has been plagued by ankle problems throughout his career and he admits it is difficult to be sidelined for long periods.
He said: "Mentally I'm strong enough to get through it but I'm like anybody else when I'm missing football.
"It's the worst feeling not being able to play."