At the end of the match Nichol approached Gregson's father with an invitation for his son to take part in trials at the club during the school summer holidays of that year.
In 1971 Gregson was noticed by West Bromwich Albion scout, Bill Emery and was invited to take part in trials at the club during the Christmas holidays of that year.
On 1 July 1974, Gregson joined West Bromwich Albion, then recently relegated to Division Two and managed by Don Howe, as an Apprentice Professional.
The 1975–76 season saw Gregson, as a 17-year-old, immediately become a regular in Albion's reserve team and in one Central League match (20 December 1975) at Burnley, he scored the equaliser in a 2–2 draw with a 25-yard shot whilst playing alongside the ex-England legend, Geoff Hurst, recently signed from Stoke City.
During the 5th round tie against Manchester United at The Hawthorns, (Tuesday, 9 March 1976) it was reported, "Summerfield's equaliser was again the result of a Lynex cross with Colin Gregson setting up the goal with a brilliant pass from midfield".
[5] During the first leg of the semi-final clash (Monday, 29 March 1976) at home to Crystal Palace, Gregson created two of Albion's goals from a corner and a free kick and also scored with a penalty in the resulting 3–2 win.
[6] In the first leg of the final (Tuesday, 27 April 1976) at Wolverhampton Wanderers, he created the first goal, scored by Kevin Summerfield, with a defence-splitting pass and was voted man of the match.
At the end of the season WBA had won the FA Youth Cup, finished second to Liverpool in the Central League, and gained promotion back to Division One.
It was reported, "Gregson, the newcomer from West Brom, was playing extremely well in midfield for Wednesday, he was instrumental in breaking up many of the dangerous home attacks".
[11] At the beginning of the 1978–79 season Maurice Setters was appointed as Wednesday's new reserve team coach after the departure of Ken Knighton to manage Sunderland.
In May 1979, Gregson left Sheffield Wednesday and spent a week in Denmark training with Randers Freja, managed by ex-Aston Villa coach, Frank Upton.
At the end of his stay, Gregson expected to be offered a two-year contract but the deal was never finalised due to the apparent abrupt departure from the club by Upton.
He missed three months of the season due to sustaining a serious knee injury but later returned for a match at Arbroath, 1 December 1979, when it was reported, "In the midfield Gregson was the pick.
Shortly afterwards he requested that his contract with the club be terminated by mutual consent, due to the excessive travelling involved from his home in Newcastle to away games in Scotland.