Former Arsenal star Keown has spoken highly of the Germany Under-21 international attacker in The Daily Mail.
The former England international has also given his verdict on Saido Berahino, Salomon Rondon and James McClean.
“For West Brom this window has been about keeping Saido Berahino,” Keown wrote in The Daily Mail. “That situation needs to be resolved.
“For a while it looked like Salomon Rondon looked like Berahino’s replacement but now they will have to work together and he looks a good player, a real handful.
“I’m not too sure about James McClean but Serge Gnabry is a good player and I think West Brom will quickly realise he’s a better player than they thought.”
Busy summer for West Bromwich Albion
West Brom made a number of signings in the summer transfer window in order to have a successful 2015-16 Premier League campaign.
Winger James McClean, central defender James Chester, striker Rickie Lambert, centre-forward Jose Rondon and centre-back Jonny Evans joined the Baggies from Wigan Athletic, Hull City, Liverpool, Zenit St. Petersburg and Manchester United respectively.
Goalkeeper Anders Lindegaard moved to West Brom on a free transfer after leaving Premier League rivals United, while winger Gnabry signed on a season-long loan deal from Arsenal.