The two have been grouped together at the Players Championship
Rory McIlroy feels current World Number 1 Dustin Johnson is comfortably the best golfer on the planet right now.
The American just missed out on a fifth win in five starts last weekend, having won his first major at the US Open in 2016.
It was his first tournament since missing the US Masters with a freak back injury after suffering a fall on the eve of the competition.
McIlroy, who last held World No 1 status in 2015, goes into this week's Players Championship closest to Johnson in the rankings.
"He's on a roll and he keeps going. I think he's got a five point lead at the top of the the world rankings at the minute which is huge," said McIlroy of Johnson.
"I can't see him falling off or dropping off. I think it's up to the other guys to try and catch him."
The duo have been paired together for the The Players Championship in Florida this week, with Justin Thomas teeing off with them.
Jason Day won the 2016 Players Championship.