Bishop has started training camp working mostly at the weak-side linebacker spot. Marvin Mitchell and rookie fourth-round draft choice Gerald Hodges from Penn State are also in the mix at that side.
Greenway contends a lot of people may be overlooking Mitchell who received some quality playing time last season.
"He played a lot and got some good experience with us," Greenway said. "I think he could have a very good year."
Mitchell, 6-foot-3, 249 pounds, was drafted by New Orleans in 2007. He played four years in New Orleans and started in the Super Bowl the year they won it all.
He played one year in Miami in 2011 and then signed with the Vikings before last season. He started two games at weak-side linebacker last year when Henderson got hurt.
"I was held back a little bit by injuries last year but I think I did OK," Mitchell said. "I'm healthy now and I'm competing for a starting spot. Everybody on the team should approach it like they're competing for a starting spot."
Second-year player Audie Cole is in the mix at outside linebacker, and Tyrone McKenzie is back for a second year with the team on the inside. Michael Mauti, another Penn State product, was drafted in the seventh round this spring and could also help at the middle linebacker spot, although he's probably more of a long-range solution.
"It's a pretty good group," Greenway said. "We just have to learn how to play alongside each other.
"It's a lot like an offensive or defensive line. You need to know what the other guy is doing and where he's going to be on a particular play. That's something we can work on in the preseason."