Coleman is impressed with the impact of the Colombian attacking midfielder, who arrived due to his prior relationship with manager Carlo Ancelotti.
And the right back believes Rodriguez has also helped striker Dominic Calvert-Lewin improve significantly.
Coleman told reporters after a win over West Brom: "Without a shadow of a doubt [James has improved Calvert-Lewin].
"He has got unbelievable quality when we can get him the ball.
"His range of passing and decision making is fantastic. We are very fortunate to have him."