Ba came close to joining Stoke in the January transfer window, but the Premier League side backed out of a move due to concerns over a knee injury.
The 25-year-old instead moved from Hoffenheim to West Ham on loan for the rest of the season.
Ba has become an instant hit at West Ham, scoring three goals in three Premier League appearances.
“There are no qualms about the decision we made,” Coates told The Sentinel.
“We would have taken the player had he passed the medical. But we were strongly advised by our medical team that it was a risk we could not take.
“You cannot spend large sums of money on a high-risk basis. We were disappointed, though, because we wanted to sign the player and the eventual decision was nothing to do with his ability.”