On 17 February 2015, Grella signed with New York Red Bulls of Major League Soccer after a successful trial spell.
Grella made his debut for New York on 8 March 2015 appearing as a starter in a 1–1 draw at Sporting Kansas City.

On 28 March 2015, Grella scored his first goal for New York and the 1,000th goal in club history in a 2–1 victory over Columbus Crew.
On 17 April 2015, Grella scored his second goal of the season for New York in a 2–0 victory over the San Jose Earthquakes.
On 5 June 2015, Grella scored his third goal of the season in a 4–2 loss versus the Houston Dynamo.
On 24 June 2015, Grella scored New York's lone goal in a 1–0 victory over Real Salt Lake.
On 1 July 2015, Grella scored his fifth goal of the season for New York, helping the Red Bulls to a 4–1 victory in the U.S. Open Cup over local rival New York Cosmos.

On 19 July 2015, Grella scored his sixth goal of the season in a 2–0 victory over Orlando City.
On 11 September 2015, Grella helped New York to a 3–2 come from behind victory over Chicago Fire SC scoring the equalizing goal.
On 18 October 2015, in a 4–1 victory over Philadelphia Union, Grella scored 7 seconds into the match, the fastest goal in MLS history, surpassing former Red Bull, Tim Cahill.
Grella added another goal in the match, helping New York clinch the Eastern Conference regular season title.
After a breakout 2015 season, supporters began calling him "Grelladinho" due to his style of play, flashy goals and ability to take on defenders with skillful dribbling.

On 19 March 2016, Grella scored his first goal of the season in helping New York to a 4-3 come from behind victory over Houston Dynamo.
On 24 April 2016, Grella scored his second goal of the season and assisted on another in helping New York to a 3-2 come from behind victory over Orlando City SC.
On April 29, 2016, Grella helped New York to a 4-0 victory against FC Dallas scoring his third goal of the season.
On 19 June 2016, Grella scored two goals in a 2-0 victory against the Seattle Sounders FC.
His performance earned him MLS Player of the week honors.
On 17 February 2015, Grella signed with New York Red Bulls of Major League Soccer after a successful trial spell. Grella made his debut for New York on 8 March 2015 appearing as a starter in a 1–1 draw at Sporting Kansas City.
On 28 March 2015, Grella scored his first goal for New York and the 1,000th goal in club history in a 2–1 victory over Columbus Crew. On 17 April 2015, Grella scored his second goal of the season for New York in a 2–0 victory over the San Jose Earthquakes. On 5 June 2015, Grella scored his third goal of the season in a 4–2 loss versus the Houston Dynamo. On 24 June 2015, Grella scored New York's lone goal in a 1–0 victory over Real Salt Lake. On 1 July 2015, Grella scored his fifth goal of the season for New York, helping the Red Bulls to a 4–1 victory in the U.S. Open Cup over local rival New York Cosmos.
On 19 July 2015, Grella scored his sixth goal of the season in a 2–0 victory over Orlando City. On 11 September 2015, Grella helped New York to a 3–2 come from behind victory over Chicago Fire SC scoring the equalizing goal. On 18 October 2015, in a 4–1 victory over Philadelphia Union, Grella scored 7 seconds into the match, the fastest goal in MLS history, surpassing former Red Bull, Tim Cahill. Grella added another goal in the match, helping New York clinch the Eastern Conference regular season title. After a breakout 2015 season, supporters began calling him "Grelladinho" due to his style of play, flashy goals and ability to take on defenders with skillful dribbling.
On 19 March 2016, Grella scored his first goal of the season in helping New York to a 4-3 come from behind victory over Houston Dynamo. On 24 April 2016, Grella scored his second goal of the season and assisted on another in helping New York to a 3-2 come from behind victory over Orlando City SC. On April 29, 2016, Grella helped New York to a 4-0 victory against FC Dallas scoring his third goal of the season. On 19 June 2016, Grella scored two goals in a 2-0 victory against the Seattle Sounders FC. His performance earned him MLS Player of the week honors.
Mike Grella