The Nigerian FA have allowed Shittu to stay with the Lions this weekend ahead of the African Cup of Nations, while fellow defender Smith has been given permission to play in the cup by parent club Tottenham.
Kenny Jackett's squad could also be bolstered by the return of winger Scott Malone, who suffered a back injury at Cardiff last month.
Midfielder Tamika Mkandawire has returned from his loan spell at Southend and is also available for selection.
But winger Chris Taylor (knee) and striker Andy Keogh (broken toe) look set to miss out again along with skipper Paul Robinson, who is still recovering from a pelvic problem.
- Sports & Recreation
- Kenny Jackett
- Scott Malone
- Tamika Mkandawire