He looked to be back on track with a buoyant start to 2018 to make the fourth round of the Australian Open, but injury has interrupted his campaign since then.

The world No.23 played with USA's Jack Sock in the doubles at Lyon in the lead-up to the French Open.

When asked if it was time for Kyrgios to start to shine, Fitzgerald warned careers can end in the blink of an eye.

"Tennis careers are short and when you're in the middle of it it feels like they're going to go a long time, but they can finish quickly," Fitzgerald said.

"So the sooner you get the results the better, the earlier you start to achieve the better.

"But in some ways it's not a bad thing to start to get success a bit later because you're older, you're more mature, you handle it easier.

"No one knows until their career is over ... but you've got to be careful. If too much time goes, career's finish quickly.

"A decent career is 10 years. Some go for a lot longer, but geez there's a lot shorter than that. I hope he can win a slam."

Fitzgerald said it would be tough for Kyrgios to "go deep" at the French, given the gruelling nature of the clay - where long rallies and matches are the norm - and the fact the Canberran only has a few doubles matches under his belt.

He said while Kyrgios might be fit, match fitness was a different thing - especially in the face of best-of-five-sets tennis at a major - and the young gun could struggle.

But getting battle hardened under those tough conditions could prove valuable for the Australian later in the year.

Wimbledon is the next major, starting on July 2, and then there's the US Open at the end of August.

Both the grass and hard-courts, respectively, suit Kyrgios better than the French clay.

"To win at the French you've got to be tough and in great shape. If he hasn't played it will be hard to possibly go deep, but I hope he plays so that accelerates his comeback," Fitzgerald said.

"If he can play at the French it means he's getting involved in real matches before the grass. So the sooner he starts the better.

"But having results at the French is probably the hardest, especially when you haven't played.

"If he plays it's a very positive thing and no one should expect too much at the French if he hasn't played for two months. The sooner the better though because that means he's healthier earlier."

Then there's the fact he's up against one-time-mate Tomic adds some spice to the encounter.

Fitzgerald had "no idea" whether Tomic getting through French qualifying meant his career was back on track, but he did feel it would bode him in good stead in the main draw.

"No idea. I don't know how to answer that. His ranking's a long way down. It can be a long way back," he said about Tomic.

"You've got to play a lot of weeks and you've got to avoid injury ... you can't play spasmodically, to get back to a higher ranking.

"[But] three matches at the French in the qualies is significant, it's good, because then there's guys in the main draw you can beat from there if you get those three under your belt."