The 20-year-old scored for England against Spain and Switzerland during the worldwide break but has been urged to quit United.
Rashford has featured at times on the flanks but with the likes of Alexis Sanchez, Anthony Martial and Jesse Lingard also in the reckoning, starts have been few and far between.
Rashford will have just a year left in his contract and former England defender Jamie Carragher has told him to quit rather than start from the bench.
And Adam believes the young forward has made the correct decision if the reports are true. "José [Mourinho] thinks the world of Marcus - he's a huge admirer of him - but he has his job to do".
"The landscape is what it is and I understand the difficulties club managers have".
Rashford subsequently went to Euro 2016 as England's boy wonder but only played a cameo role in that tournament and was then largely a substitute at this summer's World Cup.
Everton have been tipped as one of the sides Rashford could join, if he does leave United.
Rashford has managed double digits in goals the past two seasons, while Ronaldo first achieved that feat in 2005-06, as he turned 21.
"It gets to the stage where you want to play every week".
A United source was quoted by the Sun, claiming that the striker would have a hard decision to make next summer.
"He is not going to give up trying to prove himself at United but he knows he may have a big decision to make soon".
Romelu Lukaku is in front of Rashford and I don't see Rashford displacing him as long as he is there.
Rashford is now suspended for three games after being sent off for violent conduct in United's 2-0 win over Burnley before the global break.
Meanwhile, Manchester United are preparing to return to Premier League action on Saturday evening when they travel to Watford.
- UN Command head talks to N. Koreans about troop remains
- Donald Trump: China 'Under Pressure' to Make a Deal with United States
- Dele Alli and Hugo Lloris
- Canada's Freeland to hold NAFTA talks in Washington on Tuesday
- Aung San Suu Kyi defends decision to jail two journalists
- Nintendo Direct to take place tomorrow, September 13
- Apple's cheaper iPhone XR rocks bright colours
- How to pre-order the iPhone XS and iPhone XS Max
- Bank of England's Carney extends term at helm to Jan 2020
- NASA Releases Footage Of Hurricane Florence And Her 'Mike Tyson Punch'