Kevin Magnussen News
Magnussen, 26, already had a contract for 2020 while 33-year-old Grosjean had faced an uncertain future at the US-owned outfit.
The 21-year-old Monegasque lapped the Baku street circuit with a benchmark time of one minute 41.604 seconds on a sunny afternoon.
Haas team boss Guenther Steiner defended his driver, however, and said Magnussen had moved over beforehand.
The Dane lost control of his car as he crested the fast uphill sweep of the Eau Rouge corner and slammed violently into the barriers.
The four-time champion was at the top of the time-lists when the session was red-flagged with 12 minutes remaining.
The German, running on medium compound tyre in his Mercedes-powered VJM09, was 0.728s clear of Renault's Kevin Magnussen.
He replaces Venezuelan Pastor Maldonado and links up with British former GP2 champion and F1 rookie Jolyon Palmer.
Kevin Magnussen has also been seen visiting the team`s factory recently.
Formula One outfit McLaren has dropped Kevin Magnussen as its reserve driver, according to reports published on Friday.
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