France duo out of Wales clash
Thomas, 22, who started last week's 10-9 win over Ireland, suffered a hamstring strain in Racing 92's 39-35 win at Grenoble.
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"Sadly, he will be out for a few weeks," said Racing coach Laurent Labit of the five-cap wing.
O'Connor, 24, suffered a right knee injury nine minutes from the end of Montpellier's 19-16 defeat against Pau.
He is expected to be sidelined for between four and six weeks.
Agence France-Presse