T.J. Grant‘s loss will be Josh Thomson‘s gain.

With Grant medically unable to accept a planned title shot lightweight champ Anthony Pettis, Thomson will step in to challenge for the belt.

The UFC’s change in plans was revealed on FOX Sports 1’s “FOX Sports Live” shortly after Grant revealed on Twitter that he would be unable to be cleared in time for the UFC on FOX 9 event, which takes place Dec. 14 at Sleep Train Arena (formerly ARCO Arena) in Sacramento, Calif. Pettis and Thomson will compete in the evening’s headlining bout, which airs on FOX.

Thomson (20-5 MMA, 3-1 UFC) originally fought for the UFC in 2003 and picked up wins over Hermes Franca and Gerald Strebendt before suffering a memorable knockout loss to Yves Edwards at UFC 49.

Thomson would later fight for Strikeforce, where he went 9-3 in 12 appearances and held the promotion’s lightweight belt for a little more than one year.

Thomson returned to the UFC in April and turned in a scintillating performance with a second-round stoppage of the always durable Nate Diaz. After the win, and when Benson Henderson was still the UFC lightweight champ, Thomson called for the fight with Pettis a sure-to-please matchup.

“I’ll tell you right now, it’s not going the distance,” Thomson in July told MMAjunkie.com. “Stylistically, someone’s getting knocked out. The fans will win with that fight.”

Grant, who was originally expected to challenge for the title at UFC 164, was forced to withdraw from the bout after suffering a concussion in training. He was hoping to return in time to face Pettis in December. However, he’ll remained sidelined for the time being and hope to still hold a No. 1 contender spot when he returns to action.

For more on UFC on FOX 9, stay tuned to the UFC Rumors section of the site.

(Pictured: Josh Thomson)