Landman failed to overturn a six-week ban on Wednesday, having received a red card for an elbow on Jack Carty during the Dragons' defeat to Connacht in round 15 of the GUINNESS PRO12.
Despite the loss of the influential South African, who had been deputising for injured captain Lee Byrne, Coombs forged an impressive partnership with Cory Hill as Newport downed Ulster at Rodney Parade last time out.
And Coombs insists that young talents Hill and Matthew Screech, together with veteran Ian Gough, will keep the Dragons pack firing in upcoming games against Benetton Treviso and Leinster, while Landman serves out his suspension.
"Rynard is an influential player and a leader but we have got quality in the second row," Coombs told the South Wales Argus.
"Cory Hill put in a great performance against Ulster, Matthew Screech was one of our best players last season and he came off the bench while Ian Gough was watching from the stands - there's so much competition.
"Cory has got an old head on young shoulders. You wouldn't think that he is 23, he has the appearance of a 35-year-old and the mind to go with it!
"Our home performances haven't been where they need to be this season and that has been disappointing because the fans pay good money to come here and watch us.
"I spoke to the players after the Ulster game and said to make sure they enjoy their two weeks off but to not switch off, think about rugby every day and make sure you are ready when you come back."
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