Rooney urged Rashford to run at defenders
The pair spoke during the preparations for England's 3-0 win over the USA in November, which marked the end of Rooney's record-breaking international career, at which point Rashford had scored just two goals in 2018-19.
Since then, then the 21-year-old has taken his season's tally to eight in all competitions and Rooney shed light on the conversation they had about his game.
"When I went back to play for the national team against the USA, I spoke to Marcus and he was trying too much," Rooney told ESPN.
"He was trying too hard, he was working too hard, he was getting tired at the end of games.
2019 blessings pic.twitter.com/DEDY9ysAfX
— Marcus Rashford (@MarcusRashford) January 3, 2019
"But the scary thing with Marcus, when he runs at you with the ball he's impossible to defend and I reminded him to keep doing that, to just get the ball and run at defenders."
Rooney, who scored 253 goals in all competitions for United to become the club's all-time top marksman, urged his former club to have patience with midfielder Paul Pogba.
The France international has divided opinion during his second spell at Old Trafford and reportedly clashed with Jose Mourinho before his sacking in December, but Rooney indicated that Pogba will flourish if he is put under less scrutiny.
"If you don't have a good relationship with the coach, then it's difficult to be at your top if you feel like the coach is scrutinising every decision you make, every pass you make," said Rooney, who left Old Trafford to join Everton in July 2017.
"Paul Pogba will give the ball away, he'll try passes [and] it won't be the right pass at times, but you have to let him do that because two or three of them passes will create goals, will create opportunities.
"I think he found it difficult under Mourinho. I think a player and a manager with big egos clashed and the outcome was never going to be great."