The Red Devils have endured a difficult season thus far, with manager Ole Gunnar Solskjaer losing his job.
As German coach Ralf Rangnick prepares to take over the team, Parker singled out Martial and Rashford for criticism.
"You've got a young Mason Greenwood, being a young lad you wonder where he head is at," he told Talk Of The Devils.
"He was a key player a few weeks back, getting a good rapport at the back end of last season with Cavani and you could see Ronaldo was respecting what he was trying to achieve.
"I would play Greenwood in front of Rashford all day long. I'm just thinking why Rashford gets so much game time.
"You're looking at it and there is nothing coming out of it to be perfectly honest. How does Martial get the game time in Villarreal, I really don't know. It seems strange.
"Okay, if you have a bad game you have a bad game. But when you see players who don't want to work hard that is when questions need to be asked and Martial doesn't want to work hard. Rashford doesn't want to work hard. He doesn't really want to."
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