Richard Oliver will make his LV = County Championship debut for Worcestershire in the four-day clash with Glamorgan starting at New Road tomorrow (Sunday).
Opening batsman Oliver has earned his opportunity after scoring 292 not out for the Seconds against Warwickshire Seconds at Barnt Green earlier in the week.
He has also appeared in all eight completed matches by the Worcestershire Rapids in the NatWest T20 Blast – last night's game with Nottinghamshire Outlaws was washed out – and helped them put together a run of six successive wins.
Worcestershire Director of Cricket Steve Rhodes confirmed Oliver would play and said: "Anyone who makes a score like that in the second team, just about 300, deserves to get a chance in the first team, and that's what he is going to get.
"We are obviously looking forward to him hopefully carrying on that form but we've been very impressed with his run-scoring ability in league cricket, second team cricket and hopefully now in first team cricket.
"He is learning all the time about red ball cricket. He has played a handful of second team matches with the red ball but he has already got a hundred and now a double hundred.
"Hopefully he can not change anything and hopefully the occasion doesn't get the better of him but I don't think it will because he has already shown in T20 cricket that he can handle the crowds and the sort of pressure that comes with playing for the first team."
Shropshire captain Oliver initially joined the county on a six week trial but impressed sufficiently to sign a contract earlier this month until the end of the 2015 season.
England centurion Moeen Ali will also return against Glamorgan for his fifth Championship appearance of the season.
The ECB gave Worcestershire permission for Ali, who scored 108 not out in the second Investec Test against Sri Lanka, to play in the four-day game ahead of the Test series with India which starts at Trent Bridge on July 9.
Rhodes has still to finalise his side but has named a 12 man squad as Worcestershire look to maintain their unbeaten start to the season in Championship cricket.
Matt Pardoe and Ross Whiteley are excluded of the players who were in action in the 234 run win over Leicestershire at Grace Road 10 days ago.
Worcestershire (from): Mitchell, Oliver, Ali, Fell, Kervezee, Kohler-Cadmore, Cox, Leach, Shantry, Ajmal, Morris, Russell.