PHILADELPHIA -- The Giants aren't close to getting either of their left fielders back.

Hunter Pence had to push the pause button on his rehab assignment because of continued soreness in his right thumb. Mac Williamson, who seemingly had taken Pence's job, will see a concussion specialist in Pittsburgh this week. Williamson was not with the Giants in Philadelphia.

With Pence and Williamson sidelined, manager Bruce Bochy said he will continue to use a four-man outfield. Alen Hanson and Brandon Belt can also play left as needed. Gregor Blanco was Monday night's starter.

The news is a bit better for the bullpen. Mark Melancon will throw his second bullpen session on Tuesday. He did not report any problems after getting off a mound in Atlanta.

"He came out of the last one feeling good," Bochy said.

Reyes Moronta dealt with a back issue over the weekend but has been cleared to pitch Monday if needed.