In this work, we present experimental data on carbon nanotubes integration during diamond synthesis. Carbon nanotubes layers were preliminarily deposited on silicon and diamond substrates, after which the substrates were loaded into the HFCVD reactor for further growth of the diamond phase. The CVD process was held in an argon-free H₂/CH₄ working gas mixture without the use of a catalyst for carbon nanotubes growth. It is shown that in a wide range of studied working gas composition (CH₄ concentration up to 28.6 vol.%) nanotubes etched from the substrate surface before the diamond growth process began.