Updated: August 20th, 2013 9:37am
Warne: With Tonkin up, which other pitchers could get September call?

Warne: With Tonkin up, which other pitchers could get September call?

by Brandon Warne

MINNEAPOLIS -- September is just around the corner, and for the Minnesota Twins that means it'll be time for roster expansion as the season enters its final full month.

Any player on the 40-man roster can be called up in that month, though there can be procedural, professional, or other reasons as to why a player may not be promoted despite being on the 40-man roster.

Taking all of this -- as well as weighting conversations with various members of the Twins' brass -- here is a look at potential September call-ups for the local nine.

We looked Monday at positions players. This columun tackles pitcher probabilities. (Stats are through Sunday's games.)

RP Michael Tonkin

Level: Triple-A Rochester
40-man roster: Yes
Stats: 2.44 ERA, 10.1 K/9, 1.08 WHIP, 51.2 IP, 17 Saves (AA/AAA), 0 ER in 1 MLB appearance.
Analysis: Tonkin is a hard-throwing right-handed reliever who has legitimate late-inning prospects in the future. In his only appearance with the Twins, PITCHf/x recorded his fastball velocity at 93.4 mph, which trails only Glen Perkins for fastest velocity on the team. Tonkin's presence should allow Gardenhire to give Jared Burton and Casey Fien a bit more time off in September. It should also give the club a glimpse into how well the 23-year-old can handle the late-inning pressure.
Verdict: Extremely likely.

Editor's note: Tonkin was recalled Tuesday morning, replacing Kyle Gibson on the active roster. It's possible he will simply remain with the club until rosters expand September 1.

SP Scott Diamond

Level: Triple-A Rochester
40-man roster: Yes
Stats: 2-0, 2.70 ERA, 1.00 WHIP, 4.0 K/9 (AAA), 5-10, 5.52 ERA, 1.55 WHIP, 3.8 K/9
Analysis: Diamond didn't at all resemble the crafty lefty from 2012 who paced the league in walk rate and kept his ERA near 3.50 by pounding the strike zone and generating tons of groundballs. Instead, Diamond picked at the strike zone, walked nearly twice the rate of hitters he did last year and saw his already-razor-thin margin of error evaporate. The strikeouts are still nowhere to be found -- down even from last year's low rate -- but his first three starts at Triple-A were encouraging. He deserves another shot, but with a more reasonable expectation of his ceiling (No. 5 starter, not the de facto staff ace he was last season).
Verdict: Probably, and he could be a benefactor if Kyle Gibson is shut down.

SP Vance Worley

Level: Triple-A Rochester (on the disabled list)
40-man roster: Yes
Stats: 6-3, 3.88 ERA, 1.41 WHIP, 5.3 K/9 (AAA); 1-5, 7.21 ERA, 1.99 WHIP, 4.6 K/9 (MLB)
Analysis: Regression was to be expected for Worley, especially in the vein of his swinging strike rate as compared to his strikeout rate (read: not a good correlation). But Worley was absolutely blasted in his first junior circuit go-round, with twice his previous career-high home run rate and a pair of base runners for every inning he pitched. Worley, like Diamond, deserves another crack at the rotation, with a significantly stunted future projection (No. 4 starter).
Verdict: Likely, but a lot depends on health. Worley could benefit from Gibson situation.

SP Liam Hendriks

Level: Triple-A Rochester
40-man roster: Yes
Stats: 3-8, 5.08 ERA, 1.40 WHIP, 5.4 K/9 (AAA); 0-1, 3.94 ERA, 1.31 WHIP, 4.5 K/9
Analysis: It's probably fair to say that Hendriks' lack of an out pitch has caught up to him in the major leagues. He now owns a career mark of 1-11 with a 5.49 ERA. Triple-A has been unusually cruel to the Aussie right-hander this year, however, and that's not an encouraging sign for a guy who consistently outperformed what would usually be expected from a righty with a 90-mph fastball. If he comes up in September, Hendriks may be auditioning for a future minor league deal after being outrighted off the 40-man roster in the winter.
Verdict: Probably, but might be his last chance to stick in the organization.

SP Cole De Vries
Level: Double-A New Britain
40-man roster: Yes
Stats: 4-6, 5.95 ERA, 1.60 WHIP, 5.1 K/9 (Rookie, A+, AA, AAA)
Analysis: It was a terrible turn of events for De Vries, who appeared primed to make the club out of spring training before succumbing to a forearm injury. Subsequent rehab stints haven't gone well -- including an 8.00-plus ERA in 43 innings at Rochester -- and De Vries may well find himself outrighted off the 40-man in the winter. It's too bad, as De Vries is a nice story and has the local angle. But ultimately, talent wins, and at this point he isn't showing it. He may be back on a minor league deal, though.
Verdict: If he's healthy it should happen but like Hendriks this could be his swan song with the organization.

SP Pedro Hernandez

Level: Double-A New Britain
40-man roster: Yes
Stats: 2-3, 4.25 ERA, 1.38 ERA, 6.6 K/9 (AAA); 3-1, 5.54 ERA, 1.69 WHIP, 4.6 K/9
Analysis: Hernandez is brutally miscast as a lefty facing any right-handed hitters in the major leagues, as his .346/.421/.615 opposing batters' line will attest. But there's room for a lefty like him in a big league bullpen, so maybe September can be an audition for a long-term situation role. The problem is, the Twins already have Caleb Thielbar and Brian Duensing (possible non-tender) in those roles ahead of him. Hernandez is also working back from a mysterious arm injury, though he'll make a start at New Britain in the days to come.
Verdict: It could happen, but he'd have to come back as a LOOGY (lefty, one-out guy).

Other minute chances for call-ups include SP Trevor May and RP Edgar Ibarra,
May is on the 40-man roster; Ibarra is not.

Brandon Warne covers the Minnesota Twins for 1500ESPN.com. He has also contributed as a baseball analyst for Fangraphs.com and BaseballProspectus.com
Email Brandon | @Brandon_Warne