Ryan missed almost all of last year after surgery on his left hamstring following an awkward landing in the round three western derby loss to Fremantle.
The 27-year-old suffered another huge blow in January when he tore his right hamstring, leading to another round of surgery.
Ryan made a successful return to the WAFL last month, playing in the unfamiliar role of a rebounding defender.
But his performances since making his AFL return a fortnight ago have been underwhelming.
Ryan kicked just one goal from five disposals in a 37-point loss to Gold Coast, and was held goalless from seven disposals in last week's six-point loss to Essendon.
West Coast are in desperate need for Ryan to step up in Sunday's match against Collingwood at Marvel Stadium, especially with leading goalkicker Jake Waterman (concussion), gun midfielder Elliot Yeo (groin) and forward Noah Long (knee) sidelined.
"He's building. He's probably going how I expected him to," Simpson said on Friday.
"I still think that first game he played, he was genuinely nervous during the week about his body a little bit still.
"We haven't really seen him fly for a mark yet (in a game), have we?
"But he went for a pretty big 'hanger' at training yesterday, so hopefully he can do that this week."
Ryan's electric pace and high-flying marks have been a feature of his 91-game AFL career, earning him the nickname Flyin' Ryan.
Enjoy Liam Ryan's mark of the year all over again!— West Coast Eagles (@WestCoastEagles) More: https://t.co/yfgGLWAfTu pic.twitter.com/7Vo2ajksdpSeptember 23, 2019
Simpson is confident the Ryan of old will be on display once he regains confidence in his body.
"The WAFL games we played him half back, and he was hitting 32, 33 kilometres an hour," Simpson said.
"We probably haven't seen that speed and agility and flying for those marks just yet (in his AFL games this season), but I'm pretty patient.
"He's been out for a year, two significant injuries, so it's just going to have to take time."
Waterman has kicked 24 goals this season in a breakout campaign, while Yeo has put himself in All-Australian contention after hitting career-best form.
The injured duo will be sorely missed this week.
Collingwood have also been dealt a series of injury blows, with Jamie Elliott (back) the latest player to go down.
He joins a list including Dan McStay (knee), Brody Mihocek (hamstring), Beau McCreery (concussion) and Jordan De Goey (groin) on the sidelines.
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