The 18-year old striker once again stole the headlines on Sunday, after scoring the decisive goal in United's 1-0 win over rivals Manchester City.
"Marcus showed again that he is a great player in the making," said Mata.
"We all believe in him, although we must remember he's still very young and he's just arrived in the first team."
Rashford's fellow-United academy product Jesse Lingard echoed those sentiments, and revealed he is helping the young striker remain focused.
"He was buzzing, but I was keeping him grounded," joked Lingard. "He is already grounded anyway to be fair and is looking forward to the rest of his career."