Rashford is struggling in front of goal for the record 20-time top-flight champions this season, having netted once in 12 matches. But Walker said his 25-year-old England team mate still poses a threat, regardless of his current form.
The 33-year-old right-back's contract was due to expire at the end of the season amid rumours of a move to Bayern Munich.
Alexander-Arnold limped off in the closing stages of England's 1-0 win after sustaining the injury while clearing the ball.
Guardiola's delight at their 2-0 win over Aston Villa on Wednesday was tempered by injuries to playmaker Kevin De Bruyne and defender Kyle Walker.
Gabriel Jesus and defender Kyle Walker have tested positive for COVID-19, the Premier League club said on Friday.
Walker erupted for 37 points, 10 assists and six rebounds, and the Charlotte Hornets dominated the fourth quarter for a 125-118 victory.
City defender Kyle Walker has said he would have been "stupid" not to cut his post-World Cup break short and return to the club's pre-season training camp.
England defender Kyle Walker is ready to sacrifice his preferred right-back spot and play as a centre-half at his first World Cup, the 28-year-old has said.
Premier League champions Manchester City need to continue winning trophies if they want to be regarded among the great teams of English top-flight football
Trippier dropped out of the starting 11 for the next two matches but the 27-year-old has since fought his way back into the side.
The trio joined Tottenham Hotspurs players, Dele Alli, Harry Kane and Harry Winks who previously withdrawn from the national team.
Dele Alli has been given a one-game England ban after making an offensive gesture during his country's World Cup qualifier against Slovakia.