Lee Johnson revealed last week that Stewart may need injections for a shoulder injury he picked up.
The 25-year-old, who arrived on Wearside in January, started this season in tremendous form, scoring seven times in his first nine appearances of the campaign.
He is also the only Black Cat to notch a goal in Sunderland’s last three fixtures, despite that coming as a consolation goal in their 5-1 defeat to Rotherham United at the end of October.
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This is a particular worry for Phillips as he believes Johnson’s side are very reliant on the striker and that if the injury to Stewart affects his ‘physicality’, then this could derail the side’s performances in the coming weeks:
“It is a big worry because physicality is a big part of Ross Stewart’s game.” Phillips told Football Insider.
“It is going to affect him and the team in regards to the way you play to him.
“Let’s just hope that the injection does not affect his performances too much. We will all keep our fingers crossed that it doesn’t.
“He’s been brilliant for Sunderland since he has come in.
“I have always said that if Sunderland are going to get promoted this season, they need someone to chip in with 20 goals. He looks like the man to do it so they need to keep him fit.”
Both Phillips and Johnson will hope Stewart is available for Sunderland’s next match against Ipswich Town on Saturday.