Dr Jeffrey John, the gay dean of St Albans, is believed to be among the list of candidates nominated for the Bishop of Southwark.
The list of nominations is not expected to be made public until the autumn, after first being approved by the Prime Minister and the Queen. David Cameron has reportedly expressed his support for Dr John's nomination.
Reform warned that if Dr John were to be appointed, it would lead to a split in the Church of England similar to that in TEC, which saw the mass departure of traditionalist parishes after the consecration of partnered homosexual Gene Robinson as Bishop of New Hampshire in 2003.
In a statement, it said: "Dr John's teaching regarding homosexual practice is contrary to both the Bible and to the current doctrine of the Church of England.
"To appoint him Bishop would send two very clear signals. First, that the diocese of Southwark wants to walk in a different direction to the Church of England's doctrine. Second that there is now little to stop the Church of England proceeding in the same divisive direction as the Episcopal Church in the USA.
"We would support churches in Southwark seeking alternative oversight should Dr John be appointed."
Evangelical pastor the Rev Paul Dawson commented: "Our view is that it would be a very serious step for the Church of England if he were to become a bishop and that it would cause very serious damage within the Church of England itself.
"We think that if this were to happen, then the sort of split that has happened in America would be precipitated here."
While liberal Anglicans believe that homosexuals are made in God's image and therefore entitled to minister within the Church, traditionalist Anglicans believe that Scripture clearly identifies homosexuality as a sin and that homosexuals should not be entitled to enter into ordained ministry within the Church.
Orthodox group Anglican Mainstream made an "urgent" call for prayer as the Crown Nominations Commission met to consider the nominations on Monday and Tuesday.
The group's convenor Philip Giddings and Secretary Chris Sugden said the Church should not consecrate clergy whose doctrine is not fully in accord with the Church of England's teachings. They warned that consecrating Dr John would split the Anglican Communion.
"Given the contested state of the Anglican Communion, an appointment which does not meet those requirements in the Church of England would bring to an end any hope there might be of holding the Communion together," they said.
Dr John was appointed Bishop of Reading in 2003, with the support of the Archbishop of Canterbury Dr Rowan Williams. He stepped down from the post in the face of strong opposition from traditionalists in the Church of England and around the Anglican Communion.
Anglican Churches in the Global South are particularly hostile to any attempts within the Communion to embrace homosexuality.
When TEC consecrated its first partnered lesbian bishop earlier this year, some 130 Anglican leaders from the Global South issued a statement condemning the Church for its "total disregard for the mind of the Communion" in setting itself upon a course "that contradicts the plain teaching of the Holy Scriptures on matters so fundamental that they affect the very salvation of those involved".
Dr Williams said Mary Glasspool's consecration had been "regrettable" and moved to bar TEC from some of the Anglican Communion's meetings and ecumenical dialogues.