Arsenal manager Arsene Wenger admits that he 'gambled' with Abou Diaby's fitness and it could cost them.
Wenger sold Alex Song to Barcelona in the summer, in the hope that Diaby would emerge as the key figure in his midfield.
However, Diaby has been beset with injuries since joining from Auxerre in 2005 - and has started less than 100 league games for the club in that time and less than 20 in the last two years.
Wenger admits he gambled on Diaby with the likes of Jack Wilshere and Emmanuel Frimpoing poised to make their returns from injury.
"Diaby's injury record is not good," said Wenger after the France international was replaced early in the first half of Saturday's 2-1 defeat by Chelsea.
"I was concerned about him, of course. It was a gamble but I was calculating as well that Jack Wilshere was coming back.
"Francis Coquelin is here but was sick and Emmanuel Frimpong is back, while Tomas Rosicky is coming back. We have many midfield players. We don't have many physical players.
"But Mikel Arteta has shown he can be a great defensive midfield player. We'll see overall if it was a good or bad decision at the end of the season."