Yeo missed all of last year through injury, but there were promising signs earlier this season when he went through a four-week stretch averaging 20 possessions per game.
However, the 32-year-old's output has dropped markedly since then, especially over the past fortnight.
Yeo tallied only seven disposals and one clearance in the 25-point loss to Adelaide and was restricted to 12 disposals and one clearance in last week's 16-point loss to the Bulldogs.
The 227-game veteran attended plenty of centre square ball-ups in those games before spending extended stints in attack.
Yeo will come up against his former side on Saturday night when West Coast host Brisbane at Optus Stadium, and McQualter praised the hard-nut midfielder for the role's he's playing at the rebuilding Eagles.
"Yeo is the type of player - what I'm seeing is he influences the game more than what his possessions suggest," McQualter said.
"So yes, he's not a 30-possession player at the moment, but he's still having influence in our games.
"And again, it's really about the mix and how we complement each other through different areas of the ground.
"Yeo has been important to us even though he's maybe not playing his absolute best football. We still think he's a really important piece for us."
Harley Reid has undoubtedly become West Coast's No.1 midfielder, with his bash-and-crash style adding an important physical edge to the on-ball group.
McQualter isn't worried about the heavy toll on Reid's body, saying he has no plans to send the 21-year-old into attack to protect the emerging superstar.
"He's trained that he can cope with this now," McQualter said.
"He's been able to put in the work that he can cope with a full season of AFL midfield.
"So (I won't send him up forward) to protect him. But again, if we needed it to help us score or it was beneficial for the team, it's something we'd look at.
"But he's prepared himself accordingly to be able to cope with AFL midfield and he's done a terrific job so far this year."
The Lions (11-6) have won five games on the trot to shoot into second favouritism behind Fremantle for the flag.
In a quirk of the fixtures, West Coast haven't faced Brisbane since round two last year, but McQualter is well aware of the threat the Lions pose.
"The last five, six weeks they've been back to their best form," McQualter said.
"It's a great opportunity for our guys to test ourselves against a two-time reigning premiership team."
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