GEELONG defender Tom Lonergan has questioned the AFL's move to trial four field umpires during the NAB Challenge.

Umpires coach Hayden Kennedy believes adding an extra umpire to the three used during the premiership season will lead to more accurate decision-making.

But Lonergan said having any more officials on the field would be overkill.

"I don't think it is needed. I don't think it is needed at all," the 2011 premiership player told Geelong's website.

Umpires to the four in NAB Challenge trial

"I think three umpires do a good enough job. They're becoming so professional now.

"It's just another person on the field. The AFL was talking about there being too many people on the field – trainers and that sort of thing – only a year ago.

"So I'm not sure if adding another umpire would be the right thing to do."

The ever-reliable 197cm key defender is coming off an outstanding season when he was named in the initial 40-man All Australian squad.

But he believes the job for defenders will become more difficult after the introduction of new shepherding rules in marking contests for the season proper.

"We will have to evolve with the game," the 30-year-old said.

"I know the fans love seeing goals and marks and that type of thing, but defenders need to be able to do something to help their team win.

"You want to play some part of the game rather than just show up and be a witch's hat.

"I can see what they're trying to do, but we'll just have to wait and see what happens."

Lonergan said the Cats will get a better feel for the rules interpretations when their NAB Challenge campaign starts against Gold Coast in Townsville on Sunday, March 1.