Mussina, who was removed from Wednesday's game after five innings with a back strain, is "95 percent certain" to miss the two-game series in Toronto starting Tuesday night, manager Johnny Oates said.
"It's very unlikely that he'll pitch in Toronto," Oates said, "but it's not impossible."
In Mussina's place, right-hander Rick Sutcliffe would take the mound in the series opener. Left-hander Fernando Valenzuela would move up to pitch Wednesday.
The shuffle could turn out to be fortuitous for the Orioles, since it brings Valenzuela into the picture against a team that has not had good luck against left-handed starters. The Blue Jays have a 9-15 record in games against left-handed starters.
"That had nothing to do with it whatsoever," Oates said. "It's not a terrible end result, but that's not the reason that it was done."
Sutcliffe reports improvement
Sutcliffe threw on the side yesterday and reported some positive signs, but it will take more than a good workout to get him out of his midseason funk. He has been noticeably discouraged by his disappointing performance the past few weeks.
"He's struggling and he can't stand not to be helping," Oates said. "He's always been the guy we've clung to. It probably plays on his mind how it affects the team more than how it affects him personally."
Sutcliffe and pitching coach Dick Bosman said they felt they accomplished something in the bullpen before yesterday's game, but they won't know for sure until his likely start against Jack Morris on Tuesday night at SkyDome.
"I'm not going to blow it out of proportion, but we saw a lot of improvement today," Sutcliffe said. "But throwing on the side is not the same as throwing in a game."
Rookies on a roll
Rookies Jeffrey Hammonds and Damon Buford each made a big contribution in brief appearances in the game. Hammonds hit for Harold Reynolds in the eighth and drove in three runs with two singles in two at-bats. Buford had an RBI double in the ninth in his only at-bat.
The six rookie position players who have played for the Orioles this year are batting a combined .348 (32-for-92) with men in scoring position. Overall, the six (Hammonds, Buford, Jack Voigt, Paul Carey, Luis Mercedes and Sherman Obando) are batting a combined .279.
There are four teams within a half-game of first place in the American League East, the closest division race this late in the season since 1983.
Ten years ago tomorrow -- on July 26, 1983 -- the Orioles, Tigers and Yankees were locked in a three-way tie with the Blue Jays a half-game out.
Could history repeat? The winners of those two divisions met in the World Series in 1983 and the Orioles defeated the Phillies to win the world championship.
Hoiles likely to sit today
Catcher Chris Hoiles probably will get the day off today, even though the Orioles are off tomorrow. Hoiles has been suffering from knee soreness, so Oates wants to get him two days off to recuperate.
The Orioles hope that the two days off this week will give them a chance to rebound from a number of nagging injuries. Brady Anderson has been playing -- and quite well -- with a sore thumb and today's starter, Ben McDonald, will get an extra day to rest a tired shoulder.
Third baseman Tim Hulett was hit on the forearm by a pitch Friday night and experienced some redness and swelling yesterday, but he was in the starting lineup.
Hulett didn't appear to be in pain after the fastball from Twins right-hander Mike Hartley struck him near the elbow, but he said that his steely appearance was all an act.
"I didn't want to cry, so I was gritting my teeth," he said. "I remembered after I got hit that he was a little wild when they were at our place. I wish I had thought about it sooner."