The former Manchester United whiz has moved to put together the necessary paperwork in order to commit to the Reggae Boyz. However, things have been held up in recent weeks.
But McClaren said: "We are in contact all the time, with him (Greenwood) and his family.
"I am very confident he only wants to play for Jamaica. It is up to him when he moves forward with that. The ball is in his court."
The documentation required by the Jamaican Football Federation is still to be received.
There remains hope Greenwood will be available for the June World Cup qualifiers.
McClaren also declared West Ham striker Michail Antonio will be available for the June games. Antonio is working his way back after suffering a leg fracture in a car accident in December.
"Michail has come from non-league and fought his way through to play in the Premier League, in top games in Europe and for Jamaica, making an impact wherever he goes," said McClaren.
"The impact was horrendous. He is confident he will come back and is aiming for the summer period, or hopefully our World Cup qualifying group in September, October and November.
"He is a true character off the field, always bubbly and great for the squad. We miss that.
"He says the one thing he has got is motivation. When warriors have motivation, they tend to achieve their goal. His goal is to be back in the summer to help Jamaica."