"We are in the process of rebuilding our national team and it's obvious that the door is always open," Constantine said today.
India are slated to play Iran in a 2018 World Cup qualifying match at the Sree Kanteerava Stadium in Bengaluru on September 8.
They lost to Oman and Guam in their previous qualifying games earlier this year.
Asked about the criteria he has set for selecting players in the Indian team, currently ranked 156th in FIFA rankings, Constantine said, "Some players have not done enough for me while some have done what I want and have, hence, been named for the camp. I never select the national team based on how many awards (MOM) anyone wins.
"I neither select players on the basis of their contracts with their respective clubs. In some cases, it may be about the desperation of the club to get the concerned player in that particular position and it does not always determine his value to the national team.
Talking about the new additions in his probables for the Iran match, he said, "A couple comes back from injuries and it's appropriate we have a look at them.
The Briton said height was a key factor when it came to selecting the goalkeepers for his squad.
"If you look at the group of goalkeepers you will see that we have selected five of them and all have been done in collaboration with my goalkeeping coach Rogerio Ramos. You are also bound to notice one more common trait - a significant trait, in fact, and that is their height. It's one of the key factors in international level football.