Here, Press Association Sport looks at what each outcome would mean for the Three Lions.
"The picture the other day wasn't even the team, so it's even less of a drama", he said.
Dele Alli's thigh injury that was picked up against Tunisia is likely to keep him out of the side which could pave the way for Ruben Loftus-Cheek to start after impressing as a substitute against Tunisia.
Gareth Southgate's assistant was pictured at training on Thursday clutching a piece of paper with players listed in formation and in what could be interpreted as a pecking order for each position.
"In League One, you get a lot more aerial battles and the ball is in the air a lot more than on the ground, especially in the winter with the state of the pitches".
This is clearly something Southgate has worked on, with his side having taken the lead within half an hour in each of their last four fixtures - and within 15 minutes in their most recent three.
For an England team that came to the World Cup with reduced expectations, things are setting up nicely. Panama defender Adolfo Machado specializes in long, looping throw-ins to set up goals, just as Iceland midfielder Aron Gunnarsson did in the match that former national team player Alan Shearer called "the worst performance I have ever seen from an England team".
Southgate will be keen for England (1/4) to be more ruthless in front of goal on Sunday, with his side guilty of missing a number of gilt-edged chances.
Handed a winning start for the first time in a major tournament for 12 years by captain Harry Kane's injury-time victor against Tunisia, England can look forward to Sunday's meeting with Panama with a rare sense of World Cup calm.
"The referee has a hard decision", Walker said.
"I suppose there's always this element of which bits are going to be refereed and which bits aren't that seems to be open to interpretation".
England may not be world-beaters, but they should certainly have enough to see off Los Canaleros, who came through CONCACAF qualifying with a negative goal difference after winning just three of their 10 matches in the Hexagonal.
England on the other hand do have injury troubles (and we are not talking about Southgate's dislocated shoulder).
"We're really pleased with where he is at, but he wouldn't be ready for the game tomorrow".
Earlier in Group F, Mexico maintained their superb start to the World Cup with a 2-1 win over South Korea.