The 30-year-old has been sensational for the Hammers so far this term and Collins believes he is 'a world-class player.'
And that's why the centre-back is at a loss as to why Roy Hodgson is yet to pick Downing for one of his Three Lions squads.
“I know what Stewie can do, he’s a world-class player," Collins told reporters.
“Whether it’s in the middle, behind the strikers, he can play centre midfield or out wide. I don’t know how much more he has to do to get into the England team."
Meanwhile, Downing himself - who both scored and assisted once again for the Hammers during their 2-2 draw with Stoke City on Saturday - says it would be 'unbelievable' to be picked for his country, though he admits he will 'just carry on' if not.
“If he picks me it would be unbelievable,” he mused. “I’d love to play for England.
“I think the main thing for me is that I’ve got to keep playing well and if I can nick goals and create, it gives him a problem to think about.
“I know he’s been to games and is watching us, so we’ll see. That’s my attitude at the minute. If he picks me, great. If not, I’ll just carry on.”