Grealish came off the bench with exhilarating effect against Germany, laying off an assist and playing a role in another as England won 2-0.
Both of England’s goals against Germany came down the left side where Luke Shaw and top scorer Raheem Sterling have been operating brilliantly, meaning Grealish may struggle to break in.
Against Germany the Aston Villa man came on for Bukayo Saka who picked up a knock, opening the door for Grealish, while Phil Foden has missed out too, but possesses extreme threat.
“They’ve (Grealish and Foden) played for us in the past together,” Southgate said.
“We’ve just got such a strong array of attacking talent, and I’ve said all along that its impossible to keep everybody happy.
“It’s impossible to pick a team that anybody will agree with, or everybody will agree with, but we’ve got to pick the right players for the right moments. We’ve got to sense what will cause the opposition the most problems.
“You will always need runs in behind, no matter how deep a defence are. It doesn’t need to be long passes behind the defence, it can be little five yard runs to disrupt opposition defences.
“Any players who are good in one on one situations, who have that creativity, are important. We’re fortunate that we’ve got players with that profile.
“Raheem has been on fire, and his goals have made it a little more difficult for the others to get in on that left hand side that they favour.”
Meanwhile, Ukraine boss Andriy Shevchenko insisted his side has nothing to fear against world number four England, despite his side coming in as big outsiders.
Ukraine scraped into the knockout stage as the fourth of the four best third-ranked sides, before stunning Sweden in extra-time.
“They are incredibly difficult to score against but their strength shouldn’t scare us,” Shevchenko said, referring to the fact England are yet to concede this tournament.
“It should motivate us because everything is possible in football as in life and we will play our hearts out to give our fans even more to cheer about.”