Merrick believes the Venezuelan international could be key for Newcastle's Championship hopes.

However, if Vargas wants to feature in more than a few games leading into the finals, he'll have to put in some hard yards to impress the gaffer. 

"Four of five games opportunity running into the finals...would be ideal, he just has to step up his training," Merrick said.

"Ronnie is training hard, but not hard enough, he and I are going to have to have a little chat about that, but he's feeling good as well.

"I'd just like him to increase his level of training to get back sooner, because he would be quite special to use in the finals."

The Jets are guaranteed a finals berth if they win against seventh-placed Brisbane Roar next weekend, but that's the least of Merrick's ambitions.

"I've said that we'll be in the finals, the position we finish in in the finals I haven't talked about," he said.

"There's no doubt that if we're in the top four we'll have a better chance of doing well in the finals."