Varane was unveiled as a United player on the pitch at the Theatre of Dreams before Saturday's brilliant 5-1 win against Leeds United.
Martial, who has played and trained with Varane regularly over the last half a decade for the France national team, believes the centre-back will add considerable quality to the United ranks.
Talking about our summer transfer business - with Jadon Sancho the other major signing in the last few weeks - Martial told us "these are two really great players."
"Varane, I know already, of course," he continued. "And the skillset he has, I know he will bring a lot to our team, in addition to his long experience, so we are all really delighted with these two new players we have.