Did early Protestants consider transubstantiation to be idol worship? During the sacrament of the Eucharist in the Catholic denomination, it is taught that the wine becomes the actual blood of Christ.  The term is called Transubstantiation.  As far as I know, only Catholics believe this.

During the Protestant version of the communion ritual, it is believed that the wine and bread are symbols of the blood and body of Christ.  Did early Protestants believe that this ritual engages in idol worship or is there another reason why they changed the ritual?
Simple answer: Not all

The opinions of the early Reformers were divided on this issue, with Luther on one end of the spectrum:


  When asked whether Lutherans should do away with the Elevation of the Host in the liturgy, Luther consistently replied in 1544:
  By no means, for such abrogation would tend to diminish respect for the Sacrament and cause it to be undervalued . . . If Christ is truly present in the Bread, why should He not be treated with the utmost respect and even be adored?
  Joachim, one of Luther's friends, added:
  We saw how Luther bowed low at the Elevation with great devotion and reverently worshiped Christ. {Table Talk, ed. Mathesius (Leipzig ed., 1903), p.341. From Hartmann Grisar, Luther, 6 vols., London: 1917, vol. 4, pp. 239-240}


Although Luther's view differed somewhat from transubstantiation and he argued strongly against the concept of the mass as sacrifice, his view of the real presence of Christ in the host did not allow him to view it as constituting idolatry.

And Zwingli at the other end:


  If idolatry is to be banished, then one must have recourse to the pure preaching of the Word. This is exactly what Zwingli engaged to do. He began a series of discourses on the books of the New Testament, and introduced the preaching of the Word at every service. He was well called "the trumpet of the Gospel." He was perfectly successful in introducing and grounding the reformation of the Church and of the fatherland by an uninterrupted vindication of the divine authority of the Holy Scriptures. For him the Church was at its purest where the preaching was at its strongest. In God's light we see light. Where faith in Christ is thriving, idolatry will wither away. And faith comes by the hearing of the Word. Zwingli knew this and acted upon it.
  In a public disputation at Zurich, in 1523, Zwingli set forth sixty-seven theological theses outlining the reformed doctrine. Thus he declared that "Christ who offered Himself once, is for ever a perfect and satisfactory sacrifice for the sins of all believers, from which we conclude that the Mass is no sacrifice." In Romanism the Mass is the pivotal act of worship; but if the very concept of a propitiatory sacrifice in the Mass is anti-biblical, then Zwingli was not reluctant to expose it as such. The spiritual welfare of the people was at stake.
  People were to serve God in truth, not in the bondage of superstition. And if transubstantiation is false, then Romanists are evidently idolatrous. Zwingli would not tolerate this.


This was an extrememly controversial issue amongst Protestants in the 16th Century, and after an increasingly heated dispute via correspondence, the outcome of the Marburg Colloquy on this particular issue (despite agreeing with each other on everything else) was that they could not come to agreement.