Dallas Cowboys quarterback Dak Prescott and his thumb injury have been a topic of hot discussion as to when the former Mississippi State star will return. Unfortunately for Cowboys fans, that will not happen on Sunday against the Los Angeles Rams.Michael Gehlken of The Dallas Morning News reported that a person close to Prescott's situation said the 29-year-old's potential return on Sunday isn't "realistic."Michael Gehlken@GehlkenNFLCowboys QB Dak Prescott won’t play this Sunday at Rams, person familiar with situation said. His availability is considered not realistic at this stage in recovery. Cooper Rush it is again. Will Grier the backup. twitter.com/gehlkennfl/sta…Michael Gehlken@GehlkenNFLCowboys are signing QB Will Grier from practice squad to 53-man roster, person familiar with situation said. He will be No. 2 quarterback this Sunday at Rams behind Cooper Rush with Dak Prescott (thumb) missing a fourth straight game. Grier was out of standard elevations.6818Cowboys are signing QB Will Grier from practice squad to 53-man roster, person familiar with situation said. He will be No. 2 quarterback this Sunday at Rams behind Cooper Rush with Dak Prescott (thumb) missing a fourth straight game. Grier was out of standard elevations.Cowboys QB Dak Prescott won’t play this Sunday at Rams, person familiar with situation said. His availability is considered not realistic at this stage in recovery. Cooper Rush it is again. Will Grier the backup. twitter.com/gehlkennfl/sta…So Cooper Rush will once again get the start at SoFi Stadium as he looks to win his fifth consecutive start as a Cowboy.Team owner Jerry Jones spoke on Tuesday in his usual radio spot on 105.3 The Fan and said that the quarterback's injury is looking better.Jones said:“I know that it’s better. Considering the injury, considering the location of the injury, I don’t know that you could make any more progress."The overall consensus on Prescott's injury is that it is healing well and quicker due to the screws and plate that have been inserted. However, the 29-year-old still can't grip a football properly.Rush leading Dallas well in Prescott's absenceWashington Commanders v Dallas CowboysThe 28-year-old has been a backup quarterback for the entirety of his career and has stepped up well when called upon. Last year, he was thrust into the spotlight against the Minnesota Vikings and managed to pull out a victory on their home turf.This year, Rush has gotten a little more time in the hot seat and has shown up and shone out. He has won all three of his games and has 737 passing yards, four touchdowns and no interceptions. Rush also had QBR's of 95.5, 98.2 and 107.5 in those three games.Many thought the season was lost when Prescott went down with an injury, but Dallas has not faultered. In fact, they have gone the other way and improved to 3-1 on the season.The job of a backup quarterback is to keep the team afloat until the starter returns. Easier said than done, but Cooper Rush has done exactly that.Such has been his performance over the last three weeks, some sections of the Cowboys fanbase want him instilled permanently as the starter. That is something we all know will not happen, but if Rush keeps this up, he might not be a backup for much longer.If you use any of the above quotes, please credit 105.3 The Fan and H/T Sportskeeda.