Carlos Sainz's qualifying efforts in Monaco have been undone by a moment of inattention as he returned to the pits, meaning that he will have to start Sunday's race from the pit-lane rather than safely inside the top ten.

The Spaniard had out-qualified the equally impressive Max Verstappen as Toro Rosso underlined its early potential with a brace of top ten grid slots, but was adjudged to have missed an appointment with the weighbridge early in the hour-long session and was slapped with the punishment of having his times annulled.

"The driver failed to stop for weighing during Q1 when signalled to do so by the red traffic light," an FIA statement confirmed, "The car was not returned to the FIA garage and work was undertaken.

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"In accordance with Article 26.1 (iv) of the FIA Formula One Sporting Regulations, the driver is required to start from the pit-lane."

"The red light [for the weighbridge] is in a place where I could not see it easily," Sainz countered before learning of the penalty, "When I went into the pit-lane I saw it too late but, the next time, I saw it okay, so I don't think there should be too much of a problem. I mean, I couldn't see the weighbridge and I think the position of the light needs to be changed."

As a result, Sainz vacates his hard-earned eighth position, promoting both Pastor Maldonado and team-mate Verstappen and will have his work cut out on what is already the most difficult afternoon on the F1 calendar.

Romain Grosjean, the other driver facing a grid penalty after an enforced early gearbox change following the Spanish Grand Prix, will drop from eleventh to 15th as a result of Sainz's subsequent demotion.