The South American nation's squad has been severely hampered by the absent Radamel Falcao, after the Monaco man missed the final cut for Jose Pekerman's team due to a knee injury.
Also sidelined by injury for Colombia were defender Luis Amaranto Perea and striker Luis Muriel, but Santos said their first-up Group C opponents on Saturday would still provide a stern challenge.
"Of course these players (Falcao, Perea and Muriel) are very important for the team and the coach would be glad to count on them," Santos said, ahead of their clash.
"Some of them I know well.
"I don't think it is going to change the way Colombia play, because I understand that Carlos Bacca and (Teofilo) Gutierrez are very strong players and (Cristian) Zapata and (Carlos) Valdes, so they can eventually replace Perea, because they are players with a huge value.
"I cannot see a big difference, but obviously coaches like to have the best players.
"We cannot underestimate Colombia."
"This player (Mitroglou) played only the first two months, but we have seen him during some matches in the English Premier League and we understand that he is very important for our team and I believe in his qualities," Santos said.
"He is in good shape physically and day by day he gets better."
