McPharlin tore his left calf during the last quarter of the Dockers' win over St Kilda in round 15.
The injury was initially diagnosed a five-week recovery, which would have had McPharlin available for either Greater Western Sydney this Sunday or Melbourne the following week, but Lyon believes it will take a lot longer.
"No, I think on record it's going to take longer than that," Lyon said.
"I think even on Channel Seven last week, pre-game, I said he's probably going to be back round 23.
"That's probably the aim."
Fremantle a couple of injury concerns heading into Sunday's clash with the Giants.
Clancee Pearce has been ruled out with a calf injury, while David Mundy rolled an ankle against Carlton that will be monitored closely this week.
"There's slight (doubt). The expectation is he'll come up," Lyon said.
Garrick Ibbotson was a late withdrawal against the Blues with Achilles tightness last Saturday night but the in-form defender should return this week.
"He's more than likely to play," Lyon said.
"But again he sits in that bracket; we wouldn't push him over the cliff, but if he's available and fit to play he'll play."
The Dockers will be bolstered by the return of their skipper Matthew Pavlich, who has missed the last three games due to suspension.
Pavlich has played just five matches this season due to surgery on the plantaris tendon in his foot and his suspension for forceful front-on contact on West Coast's Mitch Brown in the round 16 Western Derby.
"He's been pent up," Lyon said.
"I'd imagine he's seen the form and effort the team is displaying, particularly on the weekend, and he'll be keen to come in and hold his end up.
"He wouldn't want too many hiccups from here. He wouldn't want to get suspended again for three weeks, I can tell you that."
The Dockers face GWS, Melbourne, Port Adelaide and St Kilda in the run home to September. If they win all four they will finish with 17-and-a-half wins, which could threaten for a top-two spot, but Lyon would not buy into prophecies.
"I've lost my crystal ball, it's not working at the minute," he said.
"We know everything's possible - two weeks ago against Richmond we were thinking about how we were going to stay in the eight, so things change very quickly."
