Even with Ivan Toney returning to the team, Brentford are still unable to turn the tide around as they have continue to lose crucial matches in the English Premier League and dropping closer to the relegation zone in the table. On the other hand, Chelsea are looking great in their performance lately and I think there is a very high chance for Brentford to suffer another loss against Chelsea in their next upcoming match.
It is true that with Brentford's current performance, it looks like Brentford will suffer another defeat when they face Chelsea. The reason is that in the last three matches Brentford in the Premier League has not been able to win. 
So this is a picture of Brentford performing badly this season. But even so, if you look at the Head To Head record between Brentford and Chelsea, the result is that Brentford is far superior to Chelsea. The reason is that of the five matches that Brentford and Chelsea have played, the result is that Brentford was able to win 3 matches, draw 1 and lose 1. Meanwhile, Chelsea was only able to achieve 1 win, 1 draw and 1 defeat. So if you look at the Head To Head record, Brentford is indeed superior. However, judging from the current performance of the two teams, Chelsea is indeed superior to Brentford. So I personally think there could be surprises in this match. Because on the one hand, Brentford definitely doesn't want to experience defeat again, because they are approaching the relegation zone. And on the one hand, Chelsea also definitely wants to win to at least improve their current position in the English league (11th position). For this reason, I think the match between Chelsea and Brentford will definitely be very exciting.