Geer has surrendered 22 homers on the season while also netting 20 double play grounders, as the opposition has hit .285 off him.
Geer is expected to start on Saturday and the announcement of the move could wait until then.
Will Venable was hitting .292 across 120 games with the Beavers, collecting 26 doubles, four triples and 14 homers. The outfielder, who has spent the majority of his time in centerfield, also scored 70 runs with 58 RBIs.
Venable has drawn 44 walks compared to 103 strikeouts on the season while stealing seven bases in 10 attempts. He is a .304 hitter of right-handed pitching.
He had been talked about as a September call-up, but his timetable was moved up with the injury to Scott Hairston.