To cover that hypothetical scenario, here is a scouting report on Grahl, a 25-year-old, 6'4", 205-pound German goalkeeper.
Kicker rate players on a scale of one to six: one being Marco Reus-great and six being Jacques Zoua-struggle territory.
Koen Casteels—a goalkeeper with the physical tangibles and talent to emulate compatriot Thibaut Courtois—was Hoffenheim's No. 1.
That was why Grahl flew under the radar.
When Grahl received his chance, he outperformed Casteels, who struggled throughout the season and was rated the worst Bundesliga goalkeeper by Kicker .
Grahl proved he was a brick wall in one-on-one situations.
Bayern Munich right winger Arjen Robben's placed shot was rebuffed by Grahl.
Racing through on goal, Eintracht Braunschweig centre-forward Orhan Ademi's firmly-hit shot was denied by Grahl's acrobatics.
With a diving one-handed save, Grahl thwarted Augsburg substitute Raphael Holzhauser's clear-cut scoring opportunity.
 Grahl did not play enough games to qualify for the final Kicker rankings.
However, his rating tied Nurnberg's Raphael Schafer as the fifth-best Bundesliga goalkeeper.
Lacking experience with only 11 career Bundesliga games, Grahl does not have a body of work that Arsenal management can bank on.
Is Grahl's inexplicable mistake against Borussia Dortmund a sign of things to come if he played an entire season?
|League Only||Jens Grahl||Wojciech Szczesny|
|Saves Per Goal Conceded||2.8||2.8|
|Saves Per Game||4.3||3.1|
|Clean Sheets (%)||18.2||43.2|
Grahl is headed in the direction of Schalke goalkeeper Ralf Fahrmann, who had a career-defining season after years of toiling away as a back-up and third-choice goalkeeper.
Matching Szczesny in saves per goal conceded and having a higher saves per game statistic shows Grahl has the talent to compete with Szczesny for Arsenal's No. 1 position.
Emiliano Viviano leaves Arsenal after his season ticket expires.— Hiten. (@HitenPatel13) June 28, 2014
Statistics via WhoScored.com