[Sorry in advance for the long list here. Especially for mobile app users.]
I think Lookman deserves a chance to make the left wing role his own before we look to the transfer market. It was an admittedly small sample size (579 minutes) but he contributed 0.89 expected goals + assists per 90 minutes in his time at Leipzig.
Expected goals assigns a value between 0 and 1 to each shot the player takes based on things like location and shot type. A tap in from close range would be close to 1 while a shot from halfway line would be close to 0. The aforementioned number (0.89) is the sum of expected goals from shots Lookman took and expected assists from passes Lookman made that led to a shot (adjusted to the length of one match).
To provide context for that number, here is a list of the other players who played at least 500 minutes last season and contributed at least 0.8 expected goals + assists per 90 minutes in the "Big 5" leagues (from Understat):
Obviously, there a few names that don't look like they belong there but otherwise, the list pretty much reads like the best attacking players in the top European leagues.
I'm not saying Lookman is at the level of all those names based on 579 minutes in the Bundesliga but it certainly suggests that he deserves a serious look, especially given that we already own him and all. Given the amount of work the squad needs, we should be trying to use what we have wherever possible.