Murray and Djokovic started 2017 as the world's top-two players in the ATP tennis rankings, with the duo both playing in the final of the Doha Open in January, which was won by the latter.
However, the pair have since suffered from poor form and injuries, winning just a combined three titles in the calendar year and failing to emulate their Grand Slam performances from last year.
With both players last featuring at Wimbledon, Djokovic revealed he would take the rest of the year off as he recovers from an elbow injury while Murray has also followed suit as he deals with a hip injury.
They are both, however, confirmed to return at the 2018 Australian Open and Rusedski thinks Murray will fare better upon his return, compared to the Serbian ace.
"Murray, for me, it's not mental, it's physical," Rusedski said, as quoted by Sky Sports. "If the body comes back and the hip is fine and he can get himself physically fit again, and everything is firing, he will be in the mix to win majors again.
"Djokovic, for me, however, with the elbow injury – it's such a mental question mark. He was the best player bar none when he held all the four majors [at the same time] – which no player had done since Rod Laver.
"The fall from grace he has had has been incredible – that to me is mental and that can be more difficult [to overcome] sometimes than a physical injury."
Murray is currently ranked number three while Djokovic has slipped from second to seventh in the ATP tennis rankings.