In an interview with Sky Sports News, Cavendish says that he does not believe Armitstead was doping, but that "Lizzie herself could have prevented the chaos she's in."
27-year-old Armitstead competed in the Olympic road race in Rio on Sunday but could only manage fifth, having suffered through a week under the spotlight in the build up to the race as news broke of her missed tests.
Mark Cavendish, omnium elimination, Track World Championships 2016
(Image credit: Andy Jones)
"Did she dope? No, and I don't believe she did, you know," said Cavendish.
"Was it an administrative error? Yes. Was it her fault? Yes absolutely. I know from personal experience how difficult the whereabouts system can be.
"But I have an alarm on my phone every night at 6pm and my wife has one on her phone and she makes a habit of when we talk every night she will ask me 'Have you done your whereabouts?'
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The Manxman was speaking from Rio where he's preparing for a shot at gold on the track in the men's omnium which begins on Sunday, although will appear in the team pursuit on Thursday.
Cavendish himself has recorded a missed test in the past, and says that he found it "ridiculous" that an athlete that misses three tests should get a bigger sanction than an actual failure.
"I don't think it is fair that you can get a bigger sanction for an administrative failure than for an actual doping offence. It's ridiculous," he said.
"I had a missed test with the Giro d'Italia and I think the majority of sports people have a missed test...
"You are a bit blasé until you miss your first test, but missing three?
"I think Lizzie herself could have prevented the chaos that she's in but I think she's done well to deal with it, get on her bike and show why she's world champion."
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