Bale was unveiled to Real Madrid fans at the Bernabeu on Monday after completing his £85.3m move from Tottenham.
And Coleman, while relishing having the Welshman on board, insists he will not be pressurised to select the 24-year-old who has not played since July.
Coleman said: "If he is not ready we will not risk him, regardless of whether it is a world record fee.
"We are aware a lot of people will want to see him play in the home game against Serbia.
"But he has no chance of playing 90 minutes on Friday or on Tuesday. He has not done much work in the last six weeks or two months.
"His last training session was with us before the Republic of Ireland game (in which Bale played no part in due to a foot injury).
"But he is here, he will train with us and we will assess him. For him to start on Friday would be a doubt, but that does not mean he cannot play a part."
Coleman also expressed thanks to Real Madrid for allowing Bale to join up with Wales ahead of his debut against Villarreal.
Coleman added: "Credit to them, they have not put any barriers in front of him. I know Carlo Ancelotti's right-hand man Paul Clement very well, he coached with me at Fulham, so that can help us going forward."