John Cena doesn't think he'll be a good dad.

The 40-year-old professional wrestler is engaged to his long-term partner and fellow wrestler Nikki Bella, but has said the pair are in no rush to start a family together because he's not sure if he'll be able to look after a child.

Asked if his stance on having a baby has changed, he said: ''Right now it hasn't changed. I can barely raise myself, so I just don't know how good a dad I'll be. I guess that's my biggest fear.''

The sport star has nothing but good things to say about the 33-year-old 'Total Divas' star - who is the twin sister of Brie Bella - though, as he said he's ''very fortunate'' to have her by his side.

He added to Us Weekly magazine: ''I was very fortunate to find a partner that I want to share my life with who is as driven as I am. We are literally working our tails off.''

The news comes after John recently revealed he expects to tie the knot with Nikki in 2018, as the pair - who became engaged after John got down on one knee back in April at WrestleMania 33 - are eager to marry as soon as possible, but have ''super busy'' schedules to contend with.

He said: ''The speed of everything is directly dependent on Nicole. I'm one of those guys where it took me five years to get down on one knee, so I'm ready to go, but I also know there's a lot into planning that day and since it's taken so long, it should be absolutely everything that both of us want.

''We are both super, super busy and it just has to be right. I really, really want to say I hope it's gonna be next year sometime, but also I want to do it when it's right for Nicole and she can get the most out of it as well.''