"If Turkey can make a fair case that it has jumped over [the human rights] hurdle, then to still drag one's feet or to block Turkey would undoubtedly have implications for our relationship not only with such an important country but with the Islamic world," Patten said on Tuesday.
Extensive rights reforms have recently drawn praise from European leaders and raised hopes in Ankara that the EU will decide at the end of the year to open entry talks.
However, critics in Ankara fear that Europe may be reluctant to embrace mainly Muslim Turkey on any terms.
Turkish European hopes were rattles when the Catholic Church's most senior theologian said Turkey should not attempt to join the European Union because it is a majority Muslim country with Muslim roots.
Turkey should seek its future in an association of Muslim nations rather than try to join a European community with Christian roots, the Vatican's Cardinal Joseph Ratzinger said on 11 August.
The doctrinal head of the Roman Catholic Church said Turkey had always been "in permanent contrast to Europe" and linking it to Europe would be a mistake.
Talks are close
However, EU Enlargement Commissioner Guenter Verheugen, on a fact-finding trip to Turkey before the European Commission publishes a progress report in October, signalled that Turkey was close to opening long-delayed EU entry talks, despite shortcomings in implementing political reforms.
Turkey's membership of the EU
could take a decade
In a further boost to Ankara's decades-old European Union bid, a panel of European elder statesmen in Brussels said the bloc must not delay opening talks once Turkey is deemed ready.
Patten said if Turkey met requirements on human and civil rights but was still turned down, then Europe risked sending a message to the Islamic world "which confirms much of what many people think about the inevitable clash of civilisations".
"We shouldn't lose sight of the geostrategic questions," he said in an interview during a visit to Stockholm.
If the current EU Commission, which steps down in November, does recommend that Turkey is ready, accession talks would start soon but membership of the bloc, which now has 25 member states, could take a decade or longer.
Turkey can present its case "extremely effectively" but would not be helped by US lobbying, Patten warned.
"There is sometimes a tendency to think this is an issue where America can offer Turkey membership of the European Union.
That is a temptation that should be resisted," said Patten.
Religion no hurdle
Some commissioners have voiced scepticism about absorbing Turkey's 70 million people. Dutch EU Commissioner Frits Bolkestein said this week Europe was already becoming "more Islamic".
If Turkey joined, the EU should also accept Ukraine and Belarus, which he described as "more European".
But the commission's next president, Jose Manuel Durao Barroso, and heavyweights such as German Foreign Minister Joschka Fischer, have said religion must not be a hurdle.
Patten said the EU already had a thriving Muslim population of about 12 million and that in his native Britain "more people attend mosques each week than members of the Church of England go to a service on Sunday".