WEST Coast is bracing for Daniel Venables to follow high-flying forward Liam Ryan into rehabilitation after the explosive youngster suffered a painful ankle injury against Gold Coast.
Venables had to be helped from the field in the third quarter after his leg was caught awkwardly under Jesse Joyce in a tackle.
The Eagles lost Ryan for 10-12 weeks against Geelong in round three and 19-year-old Venables' impressive start to his career looks likely to be stalled at four games.
"Venables is pretty sore. Unfortunately another lower leg injury for us," Simpson told Channel Seven.
"It's really disappointing, in particular with another young player along with Ryan, we're disappointed about that."
Venables and gun midfielder Luke Shuey (ankle) weren't sighted at Eagles training on Monday ahead of Saturday's clash with struggling Carlton at the MCG.
Jack Redden didn't join the main group after copping a bad knock to his shin against the Suns, but Simpson hoped the tough onballer would be fit to face the winless Blues.
Star spearhead Josh Kennedy was also on light duties after bagging five majors in his comeback game from ankle and knee procedures.
Kennedy completed extra running away from the main group alongside Eric Mackenzie, who is still facing an indefinite timeframe to return from stress fractures in both feet.
The Eagles could have reinforcements on the horizon, though, with big man Nathan Vardy (adductor), recruit Brendon Ah Chee (ankle) and draftee Oscar Allen (shin) expected to line up for their first games for the season with East Perth on Saturday.
After four rounds, West Coast is sitting second on the ladder and proving the naysayers wrong, with Nic Naitanui's uplifting return firing a more dynamic midfield which is supplying a hungry forward line.
WATCH: Venables injures his ankle
The Eagles are the AFL's highest scoring team, averaging better than 110 points per game, and bucking the trend with a tall attack now that Kennedy is back alongside Jack Darling, Jake Waterman and often a resting ruck.
"One thing about all those guys is they've got really high work-rate and they put good pressure on and it's been a real focus of our front half this year," Simpson said.
"Along with some smalls we think we can put enough pressure on and be dangerous in the air.
"At the moment, that's working OK but that's not to say we'll do it every week."
While Kennedy's five-goal haul received the headlines against the Suns, the dual Coleman medallist lauded Darling's excellent form and growing maturity.
Darling has kicked 12 goals, equaling his best opening month to a season, and Kennedy said the Eagles can feel his increased presence in attack.
"Jack's just grown up into a mature footballer. His leadership is something that's gone to another level," Kennedy said.
"The contest that he gives, he either wins them or he halves them, he's elite on the ground and he's been able to get onto a few kicking a few goals as well.
"It's been great to see Jack having that presence on the field. It's been something we've wanted for a while and it's finally here.
"He's in a really good space at the moment."