The world No2 came in for criticism from fellow USPGA Tour player Scott McCarron on Friday regarding his use of a pre-1990 Ping Eye 2 wedge with square grooves to exploit a loophole in a new regulation allowing only V grooves.
The Ping wedges are allowed by the game's rule-makers, the United States Golf Association and Royal & Ancient Golf Club, and approved by the PGA Tour for use in tournaments following a 1993 legal settlement with the club manufacturer that takes precedence over the governing bodies' new regulations.
Despite playing approved clubs in his opening event of 2010 at last week's Farmers Insurance Open in San Diego, McCarron told the San Francisco Chronicle: "It's cheating, and I'm appalled Phil has put it in play."
Having responded to that statement on Friday by saying he disagreed with the new rule but was within his rights to use the club in question, Mickelson was more outspoken following his third round at Torrey Pines, though he didn't mention McCarron by name in a series of interviews.
"Well, we all have our opinions on the matter, but a line was crossed, and I just was publicly slandered, and because of that I'll have to let other people handle that," Mickelson said.
Asked whether that might lead to legal action, he added: "I'm not sure. I think the (PGA] Tour will probably get on top of it."
The PGA Tour had already issued a statement on Saturday that reiterated the legality of the pre-1990 Ping clubs and cautioned against criticism of players who decided to put them in play.
"Because the use of pre-1990 Ping Eye 2 irons is permitted for play, public comments or criticisms characterising their use as a violation of the Rules of Golf as promulgated by the USGA are inappropriate at best," the PGA Tour statement said.
Told about that statement, Mickelson said it was "cool if they put that out there". He added: "Again, everybody has their opinions and so forth, and it's healthy to talk about it. But when you cross that line and slander someone publicly, that's when the Tour needs to step in – or someone else."
Mickelson has been feuding with the USGA, in particular senior technical director Dick Rugge, since last summer when it became clear the new grooves would be effective this year.
He said he was not even certain that 20-year-old wedges spun the ball more than his new wedges, yet offered no apologies because the clubs are approved for play.
"I understand black and white," Mickelson said on Friday. "And I think that myself or any other player is allowed to play those clubs because they're approved – end of story."
Instead, the story might just now be starting. McCarron, who is on the 16-man Players Advisory Council, said the wedges would be discussed tomorrow at a PAC meeting in Los Angeles with PGA Tour Commissioner Tim Finchem.
Without blaming the row, Mickelson said his driving had begun to suffer over the last couple of rounds, although after shooting a third-round two-under-par 70 to move into a tie for fifth place, he still lay four strokes behind 54-hole leader Ryuji Imada of Japan heading into Sunday's final round.
"My short game kept me in it. I didn't hit the ball the way I've been hitting it coming in," Mickelson said. "I don't feel like it's far off. Hopefully I'll make an adjustment tonight. I'll talk to Butch (Harmon] here shortly. We'll see if we can do it over the phone, otherwise I may have him come down. But at least I'm in a position now where a good round tomorrow can get it done. If I throw something in the mid to high 60s I think it has a very good chance."
Aberdeen-born Australian Michael Sim was also in the frame going into the final round in San Diego after a third-round 70 left him sharing second spot with Ben Crane, the duo trailing leader Imada by just two shots.