The former Barcelona manager, when discussing Wales' threat without superstar Gareth Bale was wary of the threat caused by the Leeds United forward's pace and movement.
The young forward has three goals and an assist to his name in six appearances the Championship this season and will certainly provide a challenge for Sergio Ramos and co.
Blessed with natural pace and stamina and averaging over 11KM run per game (more than N'Golo Kante) Roberts is without doubt a natural athlete.
Working under world renowned manager Marcelo Bielsa at Elland Road, Roberts does not run for the sake of it and his willingness to learn has impressed 'El Loco'.
Leeds legend and former dutch international Jimmy Floyd Hasselbaink said of Roberts: ''He's a good player with technical ability,'' continuing: ''He knows how to play in combinations and leads the line really well. But you need to give him time. He will have games where you won't see and him and he will have games where he will be exceptional.''
Leeds spent £2.5million (potentially rising to £4million) on the unproven youngster, signing him from West Brom in January 2018. After an injury affected first campaign Roberts is now firing for the Yorkshire club.
He has come into the starting lineup after injuries to Patrick Bamford and Kemar Roofe and his subsequent form has a Champions League winning manager fearing him.