Australia's Lleyton Hewitt insists Andy Murray and Novak Djokovic can't be underestimated going forward. Tennis superstars Murray [VIDEO] and Djokovic last played in July at Wimbledon. Murray [VIDEO] is battling with a hip injury, while Djokovic is healing an elbow problem. Both had one of their most disappointing seasons ever. The two are expected to make a comeback at the beginning of the 2018 season.

"I don't know if they'll be as dominant as they (Murray and Djokovic) were," Hewitt said per AAP, as quoted on SBS News. ''For them to pick up where they left off a couple of years ago is not that easy. But I would never write those guys off.

They've played so well in Australia in hot conditions and also in night matches on Rod Laver Arena. If they can get through that first week and give themselves a chance, then they'll be tough to beat."

Murray usually plays well in Melbourne

Murray started the year ranked at No. 1 in the world before he slumped to No. 16. The Scot captured just one title in 2017 -- in February in Dubai. The 30-year-old's 2017 campaign was affected by health issues. Murray is a three-time Grand Slam champion, as well as a two-time Olympic champion. He beat Djokovic in the 2012 US Open final to capture his maiden Grand Slam title.

Murray is expected to make his return at the Brisbane International, December 31 - January 7. The Scot has prepared in Brisbane for the Australian Open twice so far in his career -- in 2012 and 2013 -- and won it all both times.

Murray has had success at Melbourne Park so far as he is a five-time runner. The 30-year-old got defeated by Djokovic in four of his five final appearances. It will be all but easy for Murray to make a splash at Melbourne Park this coming January.

Djokovic enjoys Melbourne

Djokovic kicked off this past season ranked just behind Murray at No. 2. The Serb opened the season by winning the Doha title in the first week of the 2017 season to open his year on a strong tale. It took some time before Djokovic won his second title in 2017 in Eastbourne this past July. Djokovic wasn't at his best during this past season. The 30-year-old has since plummeted to No. 12.

2016 and 2017 Doha champion Djokovic is expected to make his comeback in Doha. The 30-year-old, who has been preparing in Qatar for the Australian Open for coupleof years now, beat Murray in this year's Doha final. Djokovic has been one of the most successful players at Melbourne Park in the last decade. Djokovic, who captured his maiden Australian Open title in 2008, is a six-time Australian Open champion. It remains to be seen can the Serb put on a strong campaign in one of his most favorable tournaments this coming January.