"I feel like as a linebacker or a D-lineman, any cut, it's a man sport -- be a man, hit me up high," Willis told CSNBayArea.com. "Hit like rams. You don't see a ram going and cutting another ram's legs. They hit head to head, pad to pad."
Williams has a broken ankle, a league source told ESPN NFL Insider Adam Schefter. He was injured when he was being cut blocked by Seattle's J.R. Sweezy midway through the first quarter Sunday.
Harbaugh said he did not know whether Williams' ankle was broken but acknowledged that Sweezy's block was "legal, the way the rules are set up."
But Willis obviously is not a fan of the rule.
"I feel like that's something the league should look into more," he told CSNBayArea.com. "You see some of that stuff, and it's uncalled for.
"You have a guy who's 300 pounds cutting a guy who's 250 pounds. Do physics to that. Hit the man up high. It should be a good collision."
Willis had eight tackles in San Francisco's 29-3 loss at rival Seattle. The star linebacker also told CSNBayArea.com that he barely avoided a cut block while defending a screen pass Sunday.
"You're not talking about a concussion and being out for two weeks," Willis said. "You're talking about being down for the rest of the season if you get hit good like that."
Niners defensive lineman Ray McDonald, who also suffered an ankle injury in the contest, agreed with Willis' feelings about legal cut blocks.
"They have to do something about that," McDonald told the website. "They're making all these rules for QBs and receivers. They got to find a way to protect the big fellas on the inside because a lot of dudes get hurt that way."
Information from ESPN.com's Terry Blount and The Associated Press was used in this report.